{"id":686,"date":"2016-11-04T03:34:49","date_gmt":"2016-11-04T03:34:49","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/microbiology\/?post_type=chapter&#038;p=686"},"modified":"2016-11-10T04:56:08","modified_gmt":"2016-11-10T04:56:08","slug":"characteristics-of-infectious-disease","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/chapter\/characteristics-of-infectious-disease\/","title":{"raw":"Characteristics of Infectious Disease","rendered":"Characteristics of Infectious Disease"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\n<ul>\r\n \t<li>Distinguish between signs and symptoms of disease<\/li>\r\n \t<li>Explain the difference between a communicable disease and a noncommunicable disease<\/li>\r\n \t<li>Compare different types of infectious diseases, including iatrogenic, nosocomial, and zoonotic diseases<\/li>\r\n \t<li>Identify and describe the stages of an acute infectious disease in terms of number of pathogens present and severity of signs and symptoms<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox examples\">\r\n<h3>Clinical Focus: Pankaj, Part 1<\/h3>\r\nPankaj, a 10-year-old boy in generally good health, went to a birthday party on Sunday with his family. He ate many different foods but was the only one in the family to eat the undercooked hot dogs served by the hosts. Monday morning, he woke up feeling achy and nauseous, and he was running a fever of 38 \u00b0C (100.4 \u00b0F). His parents, assuming Pankaj had caught the flu, made him stay home from school and limited his activities. But after 4 days, Pankaj began to experience severe headaches, and his fever spiked to 40 \u00b0C (104 \u00b0F). Growing worried, his parents finally decide to take Pankaj to a nearby clinic.\r\n<ul>\r\n \t<li>What signs and symptoms is Pankaj experiencing?<\/li>\r\n \t<li>What do these signs and symptoms tell us about the stage of Pankaj\u2019s disease?<\/li>\r\n<\/ul>\r\nWe\u2019ll return to Pankaj\u2019s example in later pages.\r\n\r\n<\/div>\r\nA <strong>disease<\/strong> is any condition in which the normal structure or functions of the body are damaged or impaired. Physical injuries or disabilities are not classified as disease, but there can be several causes for disease, including infection by a pathogen, genetics (as in many cancers or deficiencies), noninfectious environmental causes, or inappropriate immune responses. Our focus in this chapter will be on infectious diseases, although when diagnosing infectious diseases, it is always important to consider possible noninfectious causes.\r\n<h2>Signs and Symptoms of Disease<\/h2>\r\nAn <strong>infection<\/strong> is the successful colonization of a host by a microorganism. Infections can lead to disease, which causes signs and symptoms resulting in a deviation from the normal structure or functioning of the host. Microorganisms that can cause disease are known as pathogens.\r\n\r\nThe <strong>sign<\/strong><strong>s<\/strong>\u00a0of disease are objective and measurable, and can be directly observed by a clinician. Vital signs, which are used to measure the body\u2019s basic functions, include body temperature (normally 37 \u00b0C [98.6 \u00b0F]), heart rate (normally 60\u2013100 beats per minute), breathing rate (normally 12\u201318 breaths per minute), and blood pressure (normally between 90\/60 and 120\/80 mm Hg). Changes in any of the body\u2019s vital signs may be indicative of disease. For example, having a fever (a body temperature significantly higher than 37 \u00b0C or 98.6 \u00b0F) is a sign of disease because it can be measured.\r\n\r\nIn addition to changes in vital signs, other observable conditions may be considered signs of disease. For example, the presence of antibodies in a patient\u2019s serum (the liquid portion of blood that lacks clotting factors) can be observed and measured through blood tests and, therefore, can be considered a sign. However, it is important to note that the presence of antibodies is not always a sign of an active disease. Antibodies can remain in the body long after an infection has resolved; also, they may develop in response to a pathogen that is in the body but not currently causing disease.\r\n\r\nUnlike signs, <strong>symptom<\/strong><strong>s<\/strong>\u00a0of disease are subjective. Symptoms are felt or experienced by the patient, but they cannot be clinically confirmed or objectively measured. Examples of symptoms include nausea, loss of appetite, and pain. Such symptoms are important to consider when diagnosing disease, but they are subject to memory bias and are difficult to measure precisely. Some clinicians attempt to quantify symptoms by asking patients to assign a numerical value to their symptoms. For example, the Wong-Baker Faces pain-rating scale asks patients to rate their <strong>pain<\/strong> on a scale of 0\u201310. An alternative method of quantifying pain is measuring skin conductance fluctuations. These fluctuations reflect sweating due to skin sympathetic nerve activity resulting from the stressor of pain.[footnote]F. Savino et al. \"Pain Assessment in Children Undergoing Venipuncture: The Wong\u2013Baker Faces Scale Versus Skin Conductance Fluctuations.\" <em>PeerJ<\/em> 1 (2013):e37; https:\/\/peerj.com\/articles\/37\/[\/footnote]\r\n\r\nA specific group of signs and symptoms characteristic of a particular disease is called a <strong>syndrome<\/strong>. Many syndromes are named using a nomenclature based on signs and symptoms or the location of the disease. Table 1\u00a0lists some of the prefixes and suffixes commonly used in naming syndromes.\r\n<table id=\"fs-id1167585013345\" class=\"span-all\" summary=\"A table titled nomenclature of syndromes; three columns: affix, meaning, and example. The root cyto- means cell. An example is cytopenia: reduction in the number of blood cells. Hepat- means of the liver. An example is hepatitis: inflammation of the liver. \u2013pathy means disease. An example is neuropathy: a disease affecting nerves. \u2013emia means of the blood. An example is bacteremia: presence of bacteria in blood. \u2013it is means inflammation. An example is colitis: inflammation of the colon. \u2013lysis means destruction. An example is hemolysis: destruction of red blood cells. \u2013oma means tumor. An example is lymphoma: cancer of the lymphatic system. \u2013osis means diseased or abnormal condition. An example is leukocytosis: abnormally high number of white blood cells. \u2013derma means of the skin. An example is keratoderma: a thickening of the skin\">\r\n<thead>\r\n<tr valign=\"top\">\r\n<th colspan=\"3\" data-valign=\"top\" data-align=\"center\">Table 1. Nomenclature of Symptoms<\/th>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<th data-valign=\"top\" data-align=\"center\">Affix<\/th>\r\n<th data-valign=\"top\" data-align=\"center\">Meaning<\/th>\r\n<th data-valign=\"top\" data-align=\"center\">Example<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">cyto-<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">cell<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">cytopenia: reduction in the number of blood cells<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">hepat-<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">of the liver<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">hepatitis: inflammation of the liver<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">-pathy<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">disease<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">neuropathy: a disease affecting nerves<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">-emia<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">of the blood<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">bacteremia: presence of bacteria in blood<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">-itis<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">inflammation<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">colitis: inflammation of the colon<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">-lysis<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">destruction<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">hemolysis: destruction of red blood cells<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">-oma<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">tumor<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">lymphoma: cancer of the lymphatic system<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">-osis<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">diseased or abnormal condition<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">leukocytosis: abnormally high number of white blood cells<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">-derma<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">of the skin<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">keratoderma: a thickening of the skin<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\nClinicians must rely on signs and on asking questions about symptoms, medical history, and the patient\u2019s recent activities to identify a particular disease and the potential causative agent. Diagnosis is complicated by the fact that different microorganisms can cause similar signs and symptoms in a patient. For example, an individual presenting with symptoms of diarrhea may have been infected by one of a wide variety of pathogenic microorganisms. Bacterial pathogens associated with diarrheal disease include <strong><em>Vibrio cholerae<\/em><\/strong>, <strong><em>Listeria monocytogenes<\/em><\/strong>, <strong><em>Campylobacter jejuni<\/em><\/strong>, and enteropathogenic <em>Escherichia coli<\/em> (<strong>EPEC<\/strong>). Viral pathogens associated with diarrheal disease include norovirus and rotavirus. Parasitic pathogens associated with diarrhea include <strong><em>Giardia lamblia<\/em><\/strong> and <strong><em>Cryptosporidium parvum<\/em><\/strong>. Likewise, fever is indicative of many types of infection, from the <strong>common cold<\/strong> to the deadly <strong>Ebola hemorrhagic fever<\/strong>.\r\n\r\nFinally, some diseases may be <strong>asymptomatic<\/strong> or <strong>subclinical<\/strong>, meaning they do not present any noticeable signs or symptoms. For example, most individual infected with <strong>herpes simplex virus<\/strong> remain asymptomatic and are unaware that they have been infected.\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Think about It<\/h3>\r\n<ul>\r\n \t<li>Explain the difference between signs and symptoms.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<h2>Classifications of Disease<\/h2>\r\nThe World Health Organization\u2019s (WHO) <strong>International Classification of Diseases<\/strong> (ICD) is used in clinical fields to classify diseases and monitor <strong>morbidity<\/strong> (the number of cases of a disease) and <strong>mortality<\/strong> (the number of deaths due to a disease). In this section, we will introduce terminology used by the ICD (and in health-care professions in general) to describe and categorize various types of disease.\r\n\r\nAn <strong>infectious disease<\/strong> is any disease caused by the direct effect of a pathogen. A pathogen may be cellular (bacteria, parasites, and fungi) or acellular (viruses, viroids, and prions). Some infectious diseases are also <strong>communicable<\/strong>, meaning they are capable of being spread from person to person through either direct or indirect mechanisms. Some infectious communicable diseases are also considered <strong>contagious<\/strong> diseases, meaning they are easily spread from person to person. Not all contagious diseases are equally so; the degree to which a disease is contagious usually depends on how the pathogen is transmitted. For example, <strong>measles<\/strong> is a highly contagious viral disease that can be transmitted when an infected person coughs or sneezes and an uninfected person breathes in droplets containing the virus. Gonorrhea is not as contagious as measles because transmission of the pathogen (<strong><em>Neisseria gonorrhoeae<\/em><\/strong>) requires close intimate contact (usually sexual) between an infected person and an uninfected person.\r\n\r\nDiseases that are contracted as the result of a medical procedure are known as <strong>iatrogenic disease<\/strong><strong>s<\/strong>. Iatrogenic diseases can occur after procedures involving wound treatments, catheterization, or surgery if the wound or surgical site becomes contaminated. For example, an individual treated for a skin wound might acquire <strong>necrotizing fasciitis<\/strong> (an aggressive, \"flesh-eating\" disease) if bandages or other dressings became contaminated by <strong><em>Clostridium perfringens<\/em><\/strong> or one of several other bacteria that can cause this condition.\r\n\r\nDiseases acquired in hospital settings are known as <strong>nosocomial disease<\/strong><strong>s<\/strong>. Several factors contribute to the prevalence and severity of nosocomial diseases. First, sick patients bring numerous pathogens into hospitals, and some of these pathogens can be transmitted easily via improperly sterilized medical equipment, bed sheets, call buttons, door handles, or by clinicians, nurses, or therapists who do not wash their hands before touching a patient. Second, many hospital patients have weakened immune systems, making them more susceptible to infections. Compounding this, the prevalence of antibiotics in hospital settings can select for drug-resistant bacteria that can cause very serious infections that are difficult to treat.\r\n\r\nCertain infectious diseases are not transmitted between humans directly but can be transmitted from animals to humans. Such a disease is called <strong>zoonotic disease<\/strong> (or <strong>zoonosis<\/strong>). According to WHO, a zoonosis is a disease that occurs when a pathogen is transferred from a vertebrate animal to a human; however, sometimes the term is defined more broadly to include diseases transmitted by all animals (including invertebrates). For example, <strong>rabies<\/strong> is a viral zoonotic disease spread from animals to humans through bites and contact with infected saliva. Many other zoonotic diseases rely on insects or other arthropods for transmission. Examples include <strong>yellow fever<\/strong> (transmitted through the bite of mosquitoes infected with yellow fever virus) and <strong>Rocky Mountain spotted fever<\/strong> (transmitted through the bite of ticks infected with <strong><em>Rickettsia rickettsii<\/em><\/strong>).\r\n\r\nIn contrast to communicable infectious diseases, a <strong>noncommunicable<\/strong> infectious disease is not spread from one person to another. One example is <strong>tetanus<\/strong>, caused by <strong><em>Clostridium tetani<\/em><\/strong>, a bacterium that produces endospores that can survive in the soil for many years. This disease is typically only transmitted through contact with a skin wound; it cannot be passed from an infected person to another person. Similarly, <strong>Legionnaires disease<\/strong> is caused by <strong><em>Legionella pneumophila<\/em><\/strong>, a bacterium that lives within amoebae in moist locations like water-cooling towers. An individual may contract Legionnaires disease via contact with the contaminated water, but once infected, the individual cannot pass the pathogen to other individuals.\r\n\r\nIn addition to the wide variety of noncommunicable infectious diseases, <strong>noninfectious disease<\/strong><strong>s<\/strong>\u00a0(those not caused by pathogens) are an important cause of morbidity and mortality worldwide. Noninfectious diseases can be caused by a wide variety factors, including genetics, the environment, or immune system dysfunction, to name a few. For example, sickle cell anemia is an inherited disease caused by a genetic mutation that can be passed from parent to offspring (Figure\u00a01). Other types of noninfectious diseases are listed in Table 2.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1200\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03165317\/OSC_Microbio_15_01_Blood.jpg\" alt=\"a) A micrograph showing round red blood cells (erythrocytes) and a darker oval cell (Plasmodium falciparum).b) A micrograph showing round red blood cells and a \" width=\"1200\" height=\"504\" data-media-type=\"image\/jpeg\" \/> Figure\u00a01. Blood smears showing two diseases of the blood. (a) Malaria is an infectious, zoonotic disease caused by the protozoan pathogen <strong><em>Plasmodium falciparum<\/em><\/strong> (shown here) and several other species of the genus Plasmodium. It is transmitted by mosquitoes to humans. (b) Sickle cell disease is a noninfectious genetic disorder that results in abnormally shaped red blood cells, which can stick together and obstruct the flow of blood through the circulatory system. It is not caused by a pathogen, but rather a genetic mutation. (credit a: modification of work by Centers for Disease Control and Prevention; credit b: modification of work by Ed Uthman)[\/caption]\r\n<table id=\"fs-id1167584990408\" class=\"span-all\" summary=\"A table titled types of noninfectious disease; three columns: types, definition, and example. Inherited: A genetic disease; example: Sickle cell anemia. Congenital: Disease that is present at or before birth; example: Down syndrome. Degenerative: Progressive, irreversible loss of function; example: Parkinson disease (affecting central nervous system). Nutritional deficiency: Impaired body function due to lack of nutrients. Example: Scurvy (vitamin C deficiency). Endocrine: Disease involving malfunction of glands that release hormones to regulate body functions. Example: Hypothyroidism \u2013 thyroid does not produce enough thyroid hormone, which is important for metabolism. Neoplastic: Abnormal growth (benign or malignant). Example: Some forms of cancer. Idiopathic: Disease for which the cause is unknown. Example: Idiopathic juxtafoveal retinal telangiectasia (dilated, twisted blood vessels in the retina of the eye).\">\r\n<thead>\r\n<tr valign=\"top\">\r\n<th colspan=\"3\" data-valign=\"top\" data-align=\"center\">Table 2. Types of Noninfectious Diseases<\/th>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<th data-valign=\"top\" data-align=\"center\">Type<\/th>\r\n<th data-valign=\"top\" data-align=\"center\">Definition<\/th>\r\n<th data-valign=\"top\" data-align=\"center\">Example<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">Inherited<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">A genetic disease<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">Sickle cell anemia<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">Congenital<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">Disease that is present at or before birth<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">Down syndrome<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">Degenerative<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">Progressive, irreversible loss of function<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">Parkinson disease (affecting central nervous system)<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">Nutritional deficiency<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">Impaired body function due to lack of nutrients<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">Scurvy (vitamin C deficiency)<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">Endocrine<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">Disease involving malfunction of glands that release hormones to regulate body functions<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">Hypothyroidism \u2013 thyroid does not produce enough thyroid hormone, which is important for metabolism<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">Neoplastic<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">Abnormal growth (benign or malignant)<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">Some forms of cancer<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td data-valign=\"top\" data-align=\"left\">Idiopathic<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">Disease for which the cause is unknown<\/td>\r\n<td data-valign=\"top\" data-align=\"left\">Idiopathic juxtafoveal retinal telangiectasia (dilated, twisted blood vessels in the retina of the eye)<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<div class=\"textbox\">Lists of common infectious diseases can be found at the following <a href=\"https:\/\/www.cdc.gov\/diseasesconditions\/\" target=\"_blank\">Centers for Disease Control and Prevention<\/a> (CDC), <a href=\"http:\/\/www.who.int\/ith\/diseases\/en\/\" target=\"_blank\">World Health Organization<\/a> (WHO), and <a href=\"http:\/\/www.who.int\/classifications\/icd\/en\/\" target=\"_blank\">International Classification of Diseases<\/a> websites.<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Think about It<\/h3>\r\n<ul>\r\n \t<li>Describe how a disease can be infectious but not contagious.<\/li>\r\n \t<li>Explain the difference between iatrogenic disease and nosocomial disease.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<h2>Periods of Disease<\/h2>\r\nThe five <strong>periods of disease<\/strong> (sometimes referred to as stages or phases) include the incubation, prodromal, illness, decline, and convalescence periods (Figure\u00a02). The <strong>incubation period<\/strong> occurs in an acute disease after the initial entry of the pathogen into the host (patient). It is during this time the pathogen begins multiplying in the host. However, there are insufficient numbers of pathogen particles (cells or viruses) present to cause signs and symptoms of disease. Incubation periods can vary from a day or two in acute disease to months or years in chronic disease, depending upon the pathogen. Factors involved in determining the length of the incubation period are diverse, and can include strength of the pathogen, strength of the host immune defenses, site of infection, type of infection, and the size infectious dose received. During this incubation period, the patient is unaware that a disease is beginning to develop.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"700\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03165321\/OSC_Microbio_15_01_Stages.jpg\" alt=\"A graph titled \u201cPeriods of Disease\u201d with time on the X axis and two separate Y-axes: number of pathogen particles (red) and severity of symptoms (blue). Both of these lines mirror each other and have a general bell shape. The first stage is incubation period when there are few pathogens and symptoms are mild. The next stage is prodromal period when the number of pathogens is increasing and symptoms are becoming more severe. The next stage is period of illness where numbers of pathogens and symptoms both continue to increase. The next stage is period of decline in infection where the number of pathogens is decreasing and symptoms are becoming less severe. The final stage is period of convalescence when symptoms go away and the number of pathogens decrease. Note that there are still pathogens present even after there are no more symptoms of the disease. The progression of an infectious disease can be divided into five periods, which are related to the number of pathogen particles (red) and the severity of signs and symptoms (blue).\" width=\"700\" height=\"486\" data-media-type=\"image\/jpeg\" \/> Figure\u00a02. The progression of an infectious disease can be divided into five periods, which are related to the number of pathogen particles (red) and the severity of signs and symptoms (blue).[\/caption]\r\n\r\nThe <strong>prodromal period<\/strong> occurs after the incubation period. During this phase, the pathogen continues to multiply and the host begins to experience general signs and symptoms of illness, which typically result from activation of the immune system, such as fever, pain, soreness, swelling, or inflammation. Usually, such signs and symptoms are too general to indicate a particular disease. Following the prodromal period is the <strong>period of illness<\/strong>, during which the signs and symptoms of disease are most obvious and severe.\r\n\r\nThe period of illness is followed by the <strong>period of decline<\/strong>, during which the number of pathogen particles begins to decrease, and the signs and symptoms of illness begin to decline. However, during the decline period, patients may become susceptible to developing secondary infections because their immune systems have been weakened by the primary infection. The final period is known as the <strong>period of convalescence<\/strong>. During this stage, the patient generally returns to normal functions, although some diseases may inflict permanent damage that the body cannot fully repair.\r\n\r\nInfectious diseases can be contagious during all five of the periods of disease. Which periods of disease are more likely to associated with transmissibility of an infection depends upon the disease, the pathogen, and the mechanisms by which the disease develops and progresses. For example, with <strong>meningitis<\/strong> (infection of the lining of brain), the periods of infectivity depend on the type of pathogen causing the infection. Patients with bacterial meningitis are contagious during the incubation period for up to a week before the onset of the prodromal period, whereas patients with viral meningitis become contagious when the first signs and symptoms of the prodromal period appear. With many viral diseases associated with rashes (e.g., <strong>chickenpox<\/strong>, <strong>measles<\/strong>, <strong>rubella<\/strong>, <strong>roseola<\/strong>), patients are contagious during the incubation period up to a week before the rash develops. In contrast, with many respiratory infections (e.g., colds, <strong>influenza<\/strong>, <strong>diphtheria<\/strong>, <strong>strep throat<\/strong>, and <strong>pertussis<\/strong>) the patient becomes contagious with the onset of the prodromal period. Depending upon the pathogen, the disease, and the individual infected, transmission can still occur during the periods of decline, convalescence, and even long after signs and symptoms of the disease disappear. For example, an individual recovering from a diarrheal disease may continue to carry and shed the pathogen in feces for some time, posing a risk of transmission to others through direct contact or indirect contact (e.g., through contaminated objects or food).\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Think about It<\/h3>\r\n<ul>\r\n \t<li>Name some of the factors that can affect the length of the incubation period of a particular disease.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<h2>Acute and Chronic Diseases<\/h2>\r\nThe duration of the period of illness can vary greatly, depending on the pathogen, effectiveness of the immune response in the host, and any medical treatment received. For an <strong>acute disease<\/strong>, pathologic changes occur over a relatively short time (e.g., hours, days, or a few weeks) and involve a rapid onset of disease conditions. For example, <strong>influenza<\/strong> (caused by Influenzavirus) is considered an acute disease because the incubation period is approximately 1\u20132 days. Infected individuals can spread influenza to others for approximately 5 days after becoming ill. After approximately 1 week, individuals enter the period of decline.\r\n\r\nFor a <strong>chronic disease<\/strong>, pathologic changes can occur over longer time spans (e.g., months, years, or a lifetime). For example, chronic <strong>gastritis<\/strong> (inflammation of the lining of the stomach) is caused by the gram-negative bacterium <strong><em>Helicobacter pylori<\/em><\/strong>. <em>H. pylori<\/em> is able to colonize the stomach and persist in its highly acidic environment by producing the enzyme urease, which modifies the local acidity, allowing the bacteria to survive indefinitely.[footnote]J.G. Kusters et al. Pathogenesis of <em>Helicobacter pylori<\/em> Infection. <em>Clinical Microbiology Reviews<\/em> 19 no. 3 (2006):449\u2013490.[\/footnote] Consequently, <em>H. pylori<\/em> infections can recur indefinitely unless the infection is cleared using antibiotics.[footnote]N.R. Salama et al. \"Life in the Human Stomach: Persistence Strategies of the Bacterial Pathogen <em>Helicobacter pylori<\/em>.\" <em>Nature Reviews Microbiology<\/em> 11 (2013):385\u2013399.[\/footnote] <strong>Hepatitis B virus<\/strong> can cause a chronic infection in some patients who do not eliminate the virus after the acute illness. A chronic infection with hepatitis B virus is characterized by the continued production of infectious virus for 6 months or longer after the acute infection, as measured by the presence of viral antigen in blood samples.\r\n\r\nIn <strong>latent disease<\/strong><strong>s<\/strong>, as opposed to chronic infections, the causal pathogen goes dormant for extended periods of time with no active replication. Examples of diseases that go into a latent state after the acute infection include <strong>herpes<\/strong> (herpes simplex viruses [HSV-1 and HSV-2]), <strong>chickenpox<\/strong> (<strong>varicella-zoster virus<\/strong> [VZV]), and <strong>mononucleosis<\/strong> (<strong>Epstein-Barr virus<\/strong> [EBV]). HSV-1, HSV-2, and VZV evade the host immune system by residing in a latent form within cells of the nervous system for long periods of time, but they can reactivate to become active infections during times of stress and immunosuppression. For example, an initial infection by VZV may result in a case of childhood chickenpox, followed by a long period of latency. The virus may reactivate decades later, causing episodes of shingles in adulthood. EBV goes into latency in B cells of the immune system and possibly epithelial cells; it can reactivate years later to produce B-cell lymphoma.\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Think about It<\/h3>\r\n<ul>\r\n \t<li>Explain the difference between latent disease and chronic disease.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Key Concepts and Summary<\/h3>\r\n<ul>\r\n \t<li>In an <strong>infection<\/strong>, a microorganism enters a host and begins to multiply. Some infections cause <strong>disease<\/strong>, which is any deviation from the normal function or structure of the host.<\/li>\r\n \t<li><strong>Signs<\/strong>\u00a0of a disease are objective and are measured. <strong>Symptoms<\/strong>\u00a0of a disease are subjective and are reported by the patient.<\/li>\r\n \t<li>Diseases can either be <strong>noninfectious<\/strong>\u00a0(due to genetics and environment) or <strong>infectious<\/strong>\u00a0(due to pathogens). Some infectious diseases are <strong>communicable<\/strong>\u00a0(transmissible between individuals) or <strong>contagious<\/strong>\u00a0(easily transmissible between individuals); others are <strong>noncommunicable<\/strong>, but may be contracted via contact with environmental reservoirs or animals (<strong>zoonoses<\/strong>)<\/li>\r\n \t<li><strong>Nosocomial diseases<\/strong>\u00a0are contracted in hospital settings, whereas <strong>iatrogenic disease<\/strong>\u00a0are the direct result of a medical procedure<\/li>\r\n \t<li>An <strong>acute disease<\/strong>\u00a0is short in duration, whereas a <strong>chronic disease<\/strong>\u00a0lasts for months or years. <strong>Latent diseases<\/strong>\u00a0last for years, but are distinguished from chronic diseases by the lack of active replication during extended dormant periods.<\/li>\r\n \t<li>The periods of disease include the <strong>incubation period<\/strong>, the <strong>prodromal period<\/strong>, the <strong>period of illness<\/strong>, the <strong>period of decline<\/strong>, and the <strong>period of convalescence<\/strong>. These periods are marked by changes in the number of infectious agents and the severity of signs and symptoms.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Multiple Choice<\/h3>\r\nWhich of the following would be a sign of an infection?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>muscle aches<\/li>\r\n \t<li>headache<\/li>\r\n \t<li>fever<\/li>\r\n \t<li>nausea<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"497364\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"497364\"]Answer c. Fever could\u00a0be a sign of an infection.[\/hidden-answer]\r\n\r\nWhich of the following is an example of a noncommunicable infectious disease?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>infection with a respiratory virus<\/li>\r\n \t<li>food poisoning due to a preformed bacterial toxin in food<\/li>\r\n \t<li>skin infection acquired from a dog bite<\/li>\r\n \t<li>infection acquired from the stick of a contaminated needle<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"869658\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"869658\"]Answer b. Food poisoning\u00a0is an example\u00a0of a noncommunicable infectious disease.[\/hidden-answer]\r\n\r\nDuring an oral surgery, the surgeon nicked the patient\u2019s gum with a sharp instrument. This allowed <em>Streptococcus<\/em>, a bacterium normally present in the mouth, to gain access to the blood. As a result, the patient developed bacterial endocarditis (an infection of the heart). Which type of disease is this?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>iatrogenic<\/li>\r\n \t<li>nosocomial<\/li>\r\n \t<li>vectors<\/li>\r\n \t<li>zoonotic<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"954408\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"954408\"]Answer a. This is an iatrogenic disease.[\/hidden-answer]\r\n\r\nWhich period is the stage of disease during which the patient begins to present general signs and symptoms?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>convalescence<\/li>\r\n \t<li>incubation<\/li>\r\n \t<li>illness<\/li>\r\n \t<li>prodromal<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"164648\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"164648\"]Answer d. The patient begins to present general signs and symptoms during the\u00a0prodromal stage.\u00a0[\/hidden-answer]\r\n\r\nA communicable disease that can be easily transmitted from person to person is which type of disease?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>contagious<\/li>\r\n \t<li>iatrogenic<\/li>\r\n \t<li>acute<\/li>\r\n \t<li>nosocomial<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"395546\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"395546\"]Answer a. This is a contagious disease.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Fill in the Blank<\/h3>\r\nA difference between an acute disease and chronic disease is that chronic diseases have an extended period of __________.\r\n\r\n[reveal-answer q=\"25370\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"25370\"]A difference between an acute disease and chronic disease is that chronic diseases have an extended period of <strong>illness<\/strong>.[\/hidden-answer]\r\n\r\nA person steps on a rusty nail and develops tetanus. In this case, the person has acquired a(n) __________ disease.\r\n\r\n[reveal-answer q=\"60821\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"60821\"]A person steps on a rusty nail and develops tetanus. In this case, the person has acquired a\u00a0<strong>noncommunicable<\/strong> disease.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Think about It<\/h3>\r\n<ol>\r\n \t<li>Brian goes to the hospital after not feeling well for a week. He has a fever of 38 \u00b0C (100.4 \u00b0F) and complains of nausea and a constant migraine. Distinguish between the signs and symptoms of disease in Brian\u2019s case.<\/li>\r\n \t<li>Two periods of acute disease are the periods of illness and period of decline.\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>In what way are both of these periods similar?<\/li>\r\n \t<li>In terms of quantity of pathogen, in what way are these periods different?<\/li>\r\n \t<li>What initiates the period of decline?<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Critical Thinking<\/h3>\r\nIn July 2015, a report[footnote]C. Owens. \"<em>P. aeruginosa<\/em> survives in sinks 10 years after hospital outbreak.\" 2015. http:\/\/www.healio.com\/infectious-disease\/nosocomial-infections\/news\/online\/%7B5afba909-56d9-48cc-a9b0-ffe4568161e8%7D\/p-aeruginosa-survives-in-sinks-10-years-after-hospital-outbreak[\/footnote] was released indicating the gram-negative bacterium <em>Pseudomonas aeruginosa<\/em> was found on hospital sinks 10 years after the initial outbreak in a neonatal intensive care unit. <em>P. aeruginosa<\/em> usually causes localized ear and eye infections but can cause pneumonia or septicemia in vulnerable individuals like newborn babies. Explain how the current discovery of the presence of this reported <em>P. aeruginosa<\/em> could lead to a recurrence of nosocomial disease.\r\n\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<ul>\n<li>Distinguish between signs and symptoms of disease<\/li>\n<li>Explain the difference between a communicable disease and a noncommunicable disease<\/li>\n<li>Compare different types of infectious diseases, including iatrogenic, nosocomial, and zoonotic diseases<\/li>\n<li>Identify and describe the stages of an acute infectious disease in terms of number of pathogens present and severity of signs and symptoms<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox examples\">\n<h3>Clinical Focus: Pankaj, Part 1<\/h3>\n<p>Pankaj, a 10-year-old boy in generally good health, went to a birthday party on Sunday with his family. He ate many different foods but was the only one in the family to eat the undercooked hot dogs served by the hosts. Monday morning, he woke up feeling achy and nauseous, and he was running a fever of 38 \u00b0C (100.4 \u00b0F). His parents, assuming Pankaj had caught the flu, made him stay home from school and limited his activities. But after 4 days, Pankaj began to experience severe headaches, and his fever spiked to 40 \u00b0C (104 \u00b0F). Growing worried, his parents finally decide to take Pankaj to a nearby clinic.<\/p>\n<ul>\n<li>What signs and symptoms is Pankaj experiencing?<\/li>\n<li>What do these signs and symptoms tell us about the stage of Pankaj\u2019s disease?<\/li>\n<\/ul>\n<p>We\u2019ll return to Pankaj\u2019s example in later pages.<\/p>\n<\/div>\n<p>A <strong>disease<\/strong> is any condition in which the normal structure or functions of the body are damaged or impaired. Physical injuries or disabilities are not classified as disease, but there can be several causes for disease, including infection by a pathogen, genetics (as in many cancers or deficiencies), noninfectious environmental causes, or inappropriate immune responses. Our focus in this chapter will be on infectious diseases, although when diagnosing infectious diseases, it is always important to consider possible noninfectious causes.<\/p>\n<h2>Signs and Symptoms of Disease<\/h2>\n<p>An <strong>infection<\/strong> is the successful colonization of a host by a microorganism. Infections can lead to disease, which causes signs and symptoms resulting in a deviation from the normal structure or functioning of the host. Microorganisms that can cause disease are known as pathogens.<\/p>\n<p>The <strong>sign<\/strong><strong>s<\/strong>\u00a0of disease are objective and measurable, and can be directly observed by a clinician. Vital signs, which are used to measure the body\u2019s basic functions, include body temperature (normally 37 \u00b0C [98.6 \u00b0F]), heart rate (normally 60\u2013100 beats per minute), breathing rate (normally 12\u201318 breaths per minute), and blood pressure (normally between 90\/60 and 120\/80 mm Hg). Changes in any of the body\u2019s vital signs may be indicative of disease. For example, having a fever (a body temperature significantly higher than 37 \u00b0C or 98.6 \u00b0F) is a sign of disease because it can be measured.<\/p>\n<p>In addition to changes in vital signs, other observable conditions may be considered signs of disease. For example, the presence of antibodies in a patient\u2019s serum (the liquid portion of blood that lacks clotting factors) can be observed and measured through blood tests and, therefore, can be considered a sign. However, it is important to note that the presence of antibodies is not always a sign of an active disease. Antibodies can remain in the body long after an infection has resolved; also, they may develop in response to a pathogen that is in the body but not currently causing disease.<\/p>\n<p>Unlike signs, <strong>symptom<\/strong><strong>s<\/strong>\u00a0of disease are subjective. Symptoms are felt or experienced by the patient, but they cannot be clinically confirmed or objectively measured. Examples of symptoms include nausea, loss of appetite, and pain. Such symptoms are important to consider when diagnosing disease, but they are subject to memory bias and are difficult to measure precisely. Some clinicians attempt to quantify symptoms by asking patients to assign a numerical value to their symptoms. For example, the Wong-Baker Faces pain-rating scale asks patients to rate their <strong>pain<\/strong> on a scale of 0\u201310. An alternative method of quantifying pain is measuring skin conductance fluctuations. These fluctuations reflect sweating due to skin sympathetic nerve activity resulting from the stressor of pain.<a class=\"footnote\" title=\"F. Savino et al. &quot;Pain Assessment in Children Undergoing Venipuncture: The Wong\u2013Baker Faces Scale Versus Skin Conductance Fluctuations.&quot; PeerJ 1 (2013):e37; https:\/\/peerj.com\/articles\/37\/\" id=\"return-footnote-686-1\" href=\"#footnote-686-1\" aria-label=\"Footnote 1\"><sup class=\"footnote\">[1]<\/sup><\/a><\/p>\n<p>A specific group of signs and symptoms characteristic of a particular disease is called a <strong>syndrome<\/strong>. Many syndromes are named using a nomenclature based on signs and symptoms or the location of the disease. Table 1\u00a0lists some of the prefixes and suffixes commonly used in naming syndromes.<\/p>\n<table id=\"fs-id1167585013345\" class=\"span-all\" summary=\"A table titled nomenclature of syndromes; three columns: affix, meaning, and example. The root cyto- means cell. An example is cytopenia: reduction in the number of blood cells. Hepat- means of the liver. An example is hepatitis: inflammation of the liver. \u2013pathy means disease. An example is neuropathy: a disease affecting nerves. \u2013emia means of the blood. An example is bacteremia: presence of bacteria in blood. \u2013it is means inflammation. An example is colitis: inflammation of the colon. \u2013lysis means destruction. An example is hemolysis: destruction of red blood cells. \u2013oma means tumor. An example is lymphoma: cancer of the lymphatic system. \u2013osis means diseased or abnormal condition. An example is leukocytosis: abnormally high number of white blood cells. \u2013derma means of the skin. An example is keratoderma: a thickening of the skin\">\n<thead>\n<tr valign=\"top\">\n<th colspan=\"3\" data-valign=\"top\" data-align=\"center\">Table 1. Nomenclature of Symptoms<\/th>\n<\/tr>\n<tr valign=\"top\">\n<th data-valign=\"top\" data-align=\"center\">Affix<\/th>\n<th data-valign=\"top\" data-align=\"center\">Meaning<\/th>\n<th data-valign=\"top\" data-align=\"center\">Example<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">cyto-<\/td>\n<td data-valign=\"top\" data-align=\"left\">cell<\/td>\n<td data-valign=\"top\" data-align=\"left\">cytopenia: reduction in the number of blood cells<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">hepat-<\/td>\n<td data-valign=\"top\" data-align=\"left\">of the liver<\/td>\n<td data-valign=\"top\" data-align=\"left\">hepatitis: inflammation of the liver<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">-pathy<\/td>\n<td data-valign=\"top\" data-align=\"left\">disease<\/td>\n<td data-valign=\"top\" data-align=\"left\">neuropathy: a disease affecting nerves<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">-emia<\/td>\n<td data-valign=\"top\" data-align=\"left\">of the blood<\/td>\n<td data-valign=\"top\" data-align=\"left\">bacteremia: presence of bacteria in blood<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">-itis<\/td>\n<td data-valign=\"top\" data-align=\"left\">inflammation<\/td>\n<td data-valign=\"top\" data-align=\"left\">colitis: inflammation of the colon<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">-lysis<\/td>\n<td data-valign=\"top\" data-align=\"left\">destruction<\/td>\n<td data-valign=\"top\" data-align=\"left\">hemolysis: destruction of red blood cells<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">-oma<\/td>\n<td data-valign=\"top\" data-align=\"left\">tumor<\/td>\n<td data-valign=\"top\" data-align=\"left\">lymphoma: cancer of the lymphatic system<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">-osis<\/td>\n<td data-valign=\"top\" data-align=\"left\">diseased or abnormal condition<\/td>\n<td data-valign=\"top\" data-align=\"left\">leukocytosis: abnormally high number of white blood cells<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">-derma<\/td>\n<td data-valign=\"top\" data-align=\"left\">of the skin<\/td>\n<td data-valign=\"top\" data-align=\"left\">keratoderma: a thickening of the skin<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Clinicians must rely on signs and on asking questions about symptoms, medical history, and the patient\u2019s recent activities to identify a particular disease and the potential causative agent. Diagnosis is complicated by the fact that different microorganisms can cause similar signs and symptoms in a patient. For example, an individual presenting with symptoms of diarrhea may have been infected by one of a wide variety of pathogenic microorganisms. Bacterial pathogens associated with diarrheal disease include <strong><em>Vibrio cholerae<\/em><\/strong>, <strong><em>Listeria monocytogenes<\/em><\/strong>, <strong><em>Campylobacter jejuni<\/em><\/strong>, and enteropathogenic <em>Escherichia coli<\/em> (<strong>EPEC<\/strong>). Viral pathogens associated with diarrheal disease include norovirus and rotavirus. Parasitic pathogens associated with diarrhea include <strong><em>Giardia lamblia<\/em><\/strong> and <strong><em>Cryptosporidium parvum<\/em><\/strong>. Likewise, fever is indicative of many types of infection, from the <strong>common cold<\/strong> to the deadly <strong>Ebola hemorrhagic fever<\/strong>.<\/p>\n<p>Finally, some diseases may be <strong>asymptomatic<\/strong> or <strong>subclinical<\/strong>, meaning they do not present any noticeable signs or symptoms. For example, most individual infected with <strong>herpes simplex virus<\/strong> remain asymptomatic and are unaware that they have been infected.<\/p>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ul>\n<li>Explain the difference between signs and symptoms.<\/li>\n<\/ul>\n<\/div>\n<h2>Classifications of Disease<\/h2>\n<p>The World Health Organization\u2019s (WHO) <strong>International Classification of Diseases<\/strong> (ICD) is used in clinical fields to classify diseases and monitor <strong>morbidity<\/strong> (the number of cases of a disease) and <strong>mortality<\/strong> (the number of deaths due to a disease). In this section, we will introduce terminology used by the ICD (and in health-care professions in general) to describe and categorize various types of disease.<\/p>\n<p>An <strong>infectious disease<\/strong> is any disease caused by the direct effect of a pathogen. A pathogen may be cellular (bacteria, parasites, and fungi) or acellular (viruses, viroids, and prions). Some infectious diseases are also <strong>communicable<\/strong>, meaning they are capable of being spread from person to person through either direct or indirect mechanisms. Some infectious communicable diseases are also considered <strong>contagious<\/strong> diseases, meaning they are easily spread from person to person. Not all contagious diseases are equally so; the degree to which a disease is contagious usually depends on how the pathogen is transmitted. For example, <strong>measles<\/strong> is a highly contagious viral disease that can be transmitted when an infected person coughs or sneezes and an uninfected person breathes in droplets containing the virus. Gonorrhea is not as contagious as measles because transmission of the pathogen (<strong><em>Neisseria gonorrhoeae<\/em><\/strong>) requires close intimate contact (usually sexual) between an infected person and an uninfected person.<\/p>\n<p>Diseases that are contracted as the result of a medical procedure are known as <strong>iatrogenic disease<\/strong><strong>s<\/strong>. Iatrogenic diseases can occur after procedures involving wound treatments, catheterization, or surgery if the wound or surgical site becomes contaminated. For example, an individual treated for a skin wound might acquire <strong>necrotizing fasciitis<\/strong> (an aggressive, &#8220;flesh-eating&#8221; disease) if bandages or other dressings became contaminated by <strong><em>Clostridium perfringens<\/em><\/strong> or one of several other bacteria that can cause this condition.<\/p>\n<p>Diseases acquired in hospital settings are known as <strong>nosocomial disease<\/strong><strong>s<\/strong>. Several factors contribute to the prevalence and severity of nosocomial diseases. First, sick patients bring numerous pathogens into hospitals, and some of these pathogens can be transmitted easily via improperly sterilized medical equipment, bed sheets, call buttons, door handles, or by clinicians, nurses, or therapists who do not wash their hands before touching a patient. Second, many hospital patients have weakened immune systems, making them more susceptible to infections. Compounding this, the prevalence of antibiotics in hospital settings can select for drug-resistant bacteria that can cause very serious infections that are difficult to treat.<\/p>\n<p>Certain infectious diseases are not transmitted between humans directly but can be transmitted from animals to humans. Such a disease is called <strong>zoonotic disease<\/strong> (or <strong>zoonosis<\/strong>). According to WHO, a zoonosis is a disease that occurs when a pathogen is transferred from a vertebrate animal to a human; however, sometimes the term is defined more broadly to include diseases transmitted by all animals (including invertebrates). For example, <strong>rabies<\/strong> is a viral zoonotic disease spread from animals to humans through bites and contact with infected saliva. Many other zoonotic diseases rely on insects or other arthropods for transmission. Examples include <strong>yellow fever<\/strong> (transmitted through the bite of mosquitoes infected with yellow fever virus) and <strong>Rocky Mountain spotted fever<\/strong> (transmitted through the bite of ticks infected with <strong><em>Rickettsia rickettsii<\/em><\/strong>).<\/p>\n<p>In contrast to communicable infectious diseases, a <strong>noncommunicable<\/strong> infectious disease is not spread from one person to another. One example is <strong>tetanus<\/strong>, caused by <strong><em>Clostridium tetani<\/em><\/strong>, a bacterium that produces endospores that can survive in the soil for many years. This disease is typically only transmitted through contact with a skin wound; it cannot be passed from an infected person to another person. Similarly, <strong>Legionnaires disease<\/strong> is caused by <strong><em>Legionella pneumophila<\/em><\/strong>, a bacterium that lives within amoebae in moist locations like water-cooling towers. An individual may contract Legionnaires disease via contact with the contaminated water, but once infected, the individual cannot pass the pathogen to other individuals.<\/p>\n<p>In addition to the wide variety of noncommunicable infectious diseases, <strong>noninfectious disease<\/strong><strong>s<\/strong>\u00a0(those not caused by pathogens) are an important cause of morbidity and mortality worldwide. Noninfectious diseases can be caused by a wide variety factors, including genetics, the environment, or immune system dysfunction, to name a few. For example, sickle cell anemia is an inherited disease caused by a genetic mutation that can be passed from parent to offspring (Figure\u00a01). Other types of noninfectious diseases are listed in Table 2.<\/p>\n<div style=\"width: 1210px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03165317\/OSC_Microbio_15_01_Blood.jpg\" alt=\"a) A micrograph showing round red blood cells (erythrocytes) and a darker oval cell (Plasmodium falciparum).b) A micrograph showing round red blood cells and a\" width=\"1200\" height=\"504\" data-media-type=\"image\/jpeg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a01. Blood smears showing two diseases of the blood. (a) Malaria is an infectious, zoonotic disease caused by the protozoan pathogen <strong><em>Plasmodium falciparum<\/em><\/strong> (shown here) and several other species of the genus Plasmodium. It is transmitted by mosquitoes to humans. (b) Sickle cell disease is a noninfectious genetic disorder that results in abnormally shaped red blood cells, which can stick together and obstruct the flow of blood through the circulatory system. It is not caused by a pathogen, but rather a genetic mutation. (credit a: modification of work by Centers for Disease Control and Prevention; credit b: modification of work by Ed Uthman)<\/p>\n<\/div>\n<table id=\"fs-id1167584990408\" class=\"span-all\" summary=\"A table titled types of noninfectious disease; three columns: types, definition, and example. Inherited: A genetic disease; example: Sickle cell anemia. Congenital: Disease that is present at or before birth; example: Down syndrome. Degenerative: Progressive, irreversible loss of function; example: Parkinson disease (affecting central nervous system). Nutritional deficiency: Impaired body function due to lack of nutrients. Example: Scurvy (vitamin C deficiency). Endocrine: Disease involving malfunction of glands that release hormones to regulate body functions. Example: Hypothyroidism \u2013 thyroid does not produce enough thyroid hormone, which is important for metabolism. Neoplastic: Abnormal growth (benign or malignant). Example: Some forms of cancer. Idiopathic: Disease for which the cause is unknown. Example: Idiopathic juxtafoveal retinal telangiectasia (dilated, twisted blood vessels in the retina of the eye).\">\n<thead>\n<tr valign=\"top\">\n<th colspan=\"3\" data-valign=\"top\" data-align=\"center\">Table 2. Types of Noninfectious Diseases<\/th>\n<\/tr>\n<tr valign=\"top\">\n<th data-valign=\"top\" data-align=\"center\">Type<\/th>\n<th data-valign=\"top\" data-align=\"center\">Definition<\/th>\n<th data-valign=\"top\" data-align=\"center\">Example<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">Inherited<\/td>\n<td data-valign=\"top\" data-align=\"left\">A genetic disease<\/td>\n<td data-valign=\"top\" data-align=\"left\">Sickle cell anemia<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">Congenital<\/td>\n<td data-valign=\"top\" data-align=\"left\">Disease that is present at or before birth<\/td>\n<td data-valign=\"top\" data-align=\"left\">Down syndrome<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">Degenerative<\/td>\n<td data-valign=\"top\" data-align=\"left\">Progressive, irreversible loss of function<\/td>\n<td data-valign=\"top\" data-align=\"left\">Parkinson disease (affecting central nervous system)<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">Nutritional deficiency<\/td>\n<td data-valign=\"top\" data-align=\"left\">Impaired body function due to lack of nutrients<\/td>\n<td data-valign=\"top\" data-align=\"left\">Scurvy (vitamin C deficiency)<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">Endocrine<\/td>\n<td data-valign=\"top\" data-align=\"left\">Disease involving malfunction of glands that release hormones to regulate body functions<\/td>\n<td data-valign=\"top\" data-align=\"left\">Hypothyroidism \u2013 thyroid does not produce enough thyroid hormone, which is important for metabolism<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">Neoplastic<\/td>\n<td data-valign=\"top\" data-align=\"left\">Abnormal growth (benign or malignant)<\/td>\n<td data-valign=\"top\" data-align=\"left\">Some forms of cancer<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td data-valign=\"top\" data-align=\"left\">Idiopathic<\/td>\n<td data-valign=\"top\" data-align=\"left\">Disease for which the cause is unknown<\/td>\n<td data-valign=\"top\" data-align=\"left\">Idiopathic juxtafoveal retinal telangiectasia (dilated, twisted blood vessels in the retina of the eye)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<div class=\"textbox\">Lists of common infectious diseases can be found at the following <a href=\"https:\/\/www.cdc.gov\/diseasesconditions\/\" target=\"_blank\">Centers for Disease Control and Prevention<\/a> (CDC), <a href=\"http:\/\/www.who.int\/ith\/diseases\/en\/\" target=\"_blank\">World Health Organization<\/a> (WHO), and <a href=\"http:\/\/www.who.int\/classifications\/icd\/en\/\" target=\"_blank\">International Classification of Diseases<\/a> websites.<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ul>\n<li>Describe how a disease can be infectious but not contagious.<\/li>\n<li>Explain the difference between iatrogenic disease and nosocomial disease.<\/li>\n<\/ul>\n<\/div>\n<h2>Periods of Disease<\/h2>\n<p>The five <strong>periods of disease<\/strong> (sometimes referred to as stages or phases) include the incubation, prodromal, illness, decline, and convalescence periods (Figure\u00a02). The <strong>incubation period<\/strong> occurs in an acute disease after the initial entry of the pathogen into the host (patient). It is during this time the pathogen begins multiplying in the host. However, there are insufficient numbers of pathogen particles (cells or viruses) present to cause signs and symptoms of disease. Incubation periods can vary from a day or two in acute disease to months or years in chronic disease, depending upon the pathogen. Factors involved in determining the length of the incubation period are diverse, and can include strength of the pathogen, strength of the host immune defenses, site of infection, type of infection, and the size infectious dose received. During this incubation period, the patient is unaware that a disease is beginning to develop.<\/p>\n<div style=\"width: 710px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03165321\/OSC_Microbio_15_01_Stages.jpg\" alt=\"A graph titled \u201cPeriods of Disease\u201d with time on the X axis and two separate Y-axes: number of pathogen particles (red) and severity of symptoms (blue). Both of these lines mirror each other and have a general bell shape. The first stage is incubation period when there are few pathogens and symptoms are mild. The next stage is prodromal period when the number of pathogens is increasing and symptoms are becoming more severe. The next stage is period of illness where numbers of pathogens and symptoms both continue to increase. The next stage is period of decline in infection where the number of pathogens is decreasing and symptoms are becoming less severe. The final stage is period of convalescence when symptoms go away and the number of pathogens decrease. Note that there are still pathogens present even after there are no more symptoms of the disease. The progression of an infectious disease can be divided into five periods, which are related to the number of pathogen particles (red) and the severity of signs and symptoms (blue).\" width=\"700\" height=\"486\" data-media-type=\"image\/jpeg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a02. The progression of an infectious disease can be divided into five periods, which are related to the number of pathogen particles (red) and the severity of signs and symptoms (blue).<\/p>\n<\/div>\n<p>The <strong>prodromal period<\/strong> occurs after the incubation period. During this phase, the pathogen continues to multiply and the host begins to experience general signs and symptoms of illness, which typically result from activation of the immune system, such as fever, pain, soreness, swelling, or inflammation. Usually, such signs and symptoms are too general to indicate a particular disease. Following the prodromal period is the <strong>period of illness<\/strong>, during which the signs and symptoms of disease are most obvious and severe.<\/p>\n<p>The period of illness is followed by the <strong>period of decline<\/strong>, during which the number of pathogen particles begins to decrease, and the signs and symptoms of illness begin to decline. However, during the decline period, patients may become susceptible to developing secondary infections because their immune systems have been weakened by the primary infection. The final period is known as the <strong>period of convalescence<\/strong>. During this stage, the patient generally returns to normal functions, although some diseases may inflict permanent damage that the body cannot fully repair.<\/p>\n<p>Infectious diseases can be contagious during all five of the periods of disease. Which periods of disease are more likely to associated with transmissibility of an infection depends upon the disease, the pathogen, and the mechanisms by which the disease develops and progresses. For example, with <strong>meningitis<\/strong> (infection of the lining of brain), the periods of infectivity depend on the type of pathogen causing the infection. Patients with bacterial meningitis are contagious during the incubation period for up to a week before the onset of the prodromal period, whereas patients with viral meningitis become contagious when the first signs and symptoms of the prodromal period appear. With many viral diseases associated with rashes (e.g., <strong>chickenpox<\/strong>, <strong>measles<\/strong>, <strong>rubella<\/strong>, <strong>roseola<\/strong>), patients are contagious during the incubation period up to a week before the rash develops. In contrast, with many respiratory infections (e.g., colds, <strong>influenza<\/strong>, <strong>diphtheria<\/strong>, <strong>strep throat<\/strong>, and <strong>pertussis<\/strong>) the patient becomes contagious with the onset of the prodromal period. Depending upon the pathogen, the disease, and the individual infected, transmission can still occur during the periods of decline, convalescence, and even long after signs and symptoms of the disease disappear. For example, an individual recovering from a diarrheal disease may continue to carry and shed the pathogen in feces for some time, posing a risk of transmission to others through direct contact or indirect contact (e.g., through contaminated objects or food).<\/p>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ul>\n<li>Name some of the factors that can affect the length of the incubation period of a particular disease.<\/li>\n<\/ul>\n<\/div>\n<h2>Acute and Chronic Diseases<\/h2>\n<p>The duration of the period of illness can vary greatly, depending on the pathogen, effectiveness of the immune response in the host, and any medical treatment received. For an <strong>acute disease<\/strong>, pathologic changes occur over a relatively short time (e.g., hours, days, or a few weeks) and involve a rapid onset of disease conditions. For example, <strong>influenza<\/strong> (caused by Influenzavirus) is considered an acute disease because the incubation period is approximately 1\u20132 days. Infected individuals can spread influenza to others for approximately 5 days after becoming ill. After approximately 1 week, individuals enter the period of decline.<\/p>\n<p>For a <strong>chronic disease<\/strong>, pathologic changes can occur over longer time spans (e.g., months, years, or a lifetime). For example, chronic <strong>gastritis<\/strong> (inflammation of the lining of the stomach) is caused by the gram-negative bacterium <strong><em>Helicobacter pylori<\/em><\/strong>. <em>H. pylori<\/em> is able to colonize the stomach and persist in its highly acidic environment by producing the enzyme urease, which modifies the local acidity, allowing the bacteria to survive indefinitely.<a class=\"footnote\" title=\"J.G. Kusters et al. Pathogenesis of Helicobacter pylori Infection. Clinical Microbiology Reviews 19 no. 3 (2006):449\u2013490.\" id=\"return-footnote-686-2\" href=\"#footnote-686-2\" aria-label=\"Footnote 2\"><sup class=\"footnote\">[2]<\/sup><\/a> Consequently, <em>H. pylori<\/em> infections can recur indefinitely unless the infection is cleared using antibiotics.<a class=\"footnote\" title=\"N.R. Salama et al. &quot;Life in the Human Stomach: Persistence Strategies of the Bacterial Pathogen Helicobacter pylori.&quot; Nature Reviews Microbiology 11 (2013):385\u2013399.\" id=\"return-footnote-686-3\" href=\"#footnote-686-3\" aria-label=\"Footnote 3\"><sup class=\"footnote\">[3]<\/sup><\/a> <strong>Hepatitis B virus<\/strong> can cause a chronic infection in some patients who do not eliminate the virus after the acute illness. A chronic infection with hepatitis B virus is characterized by the continued production of infectious virus for 6 months or longer after the acute infection, as measured by the presence of viral antigen in blood samples.<\/p>\n<p>In <strong>latent disease<\/strong><strong>s<\/strong>, as opposed to chronic infections, the causal pathogen goes dormant for extended periods of time with no active replication. Examples of diseases that go into a latent state after the acute infection include <strong>herpes<\/strong> (herpes simplex viruses [HSV-1 and HSV-2]), <strong>chickenpox<\/strong> (<strong>varicella-zoster virus<\/strong> [VZV]), and <strong>mononucleosis<\/strong> (<strong>Epstein-Barr virus<\/strong> [EBV]). HSV-1, HSV-2, and VZV evade the host immune system by residing in a latent form within cells of the nervous system for long periods of time, but they can reactivate to become active infections during times of stress and immunosuppression. For example, an initial infection by VZV may result in a case of childhood chickenpox, followed by a long period of latency. The virus may reactivate decades later, causing episodes of shingles in adulthood. EBV goes into latency in B cells of the immune system and possibly epithelial cells; it can reactivate years later to produce B-cell lymphoma.<\/p>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ul>\n<li>Explain the difference between latent disease and chronic disease.<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Key Concepts and Summary<\/h3>\n<ul>\n<li>In an <strong>infection<\/strong>, a microorganism enters a host and begins to multiply. Some infections cause <strong>disease<\/strong>, which is any deviation from the normal function or structure of the host.<\/li>\n<li><strong>Signs<\/strong>\u00a0of a disease are objective and are measured. <strong>Symptoms<\/strong>\u00a0of a disease are subjective and are reported by the patient.<\/li>\n<li>Diseases can either be <strong>noninfectious<\/strong>\u00a0(due to genetics and environment) or <strong>infectious<\/strong>\u00a0(due to pathogens). Some infectious diseases are <strong>communicable<\/strong>\u00a0(transmissible between individuals) or <strong>contagious<\/strong>\u00a0(easily transmissible between individuals); others are <strong>noncommunicable<\/strong>, but may be contracted via contact with environmental reservoirs or animals (<strong>zoonoses<\/strong>)<\/li>\n<li><strong>Nosocomial diseases<\/strong>\u00a0are contracted in hospital settings, whereas <strong>iatrogenic disease<\/strong>\u00a0are the direct result of a medical procedure<\/li>\n<li>An <strong>acute disease<\/strong>\u00a0is short in duration, whereas a <strong>chronic disease<\/strong>\u00a0lasts for months or years. <strong>Latent diseases<\/strong>\u00a0last for years, but are distinguished from chronic diseases by the lack of active replication during extended dormant periods.<\/li>\n<li>The periods of disease include the <strong>incubation period<\/strong>, the <strong>prodromal period<\/strong>, the <strong>period of illness<\/strong>, the <strong>period of decline<\/strong>, and the <strong>period of convalescence<\/strong>. These periods are marked by changes in the number of infectious agents and the severity of signs and symptoms.<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Multiple Choice<\/h3>\n<p>Which of the following would be a sign of an infection?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>muscle aches<\/li>\n<li>headache<\/li>\n<li>fever<\/li>\n<li>nausea<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q497364\">Show Answer<\/span><\/p>\n<div id=\"q497364\" class=\"hidden-answer\" style=\"display: none\">Answer c. Fever could\u00a0be a sign of an infection.<\/div>\n<\/div>\n<p>Which of the following is an example of a noncommunicable infectious disease?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>infection with a respiratory virus<\/li>\n<li>food poisoning due to a preformed bacterial toxin in food<\/li>\n<li>skin infection acquired from a dog bite<\/li>\n<li>infection acquired from the stick of a contaminated needle<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q869658\">Show Answer<\/span><\/p>\n<div id=\"q869658\" class=\"hidden-answer\" style=\"display: none\">Answer b. Food poisoning\u00a0is an example\u00a0of a noncommunicable infectious disease.<\/div>\n<\/div>\n<p>During an oral surgery, the surgeon nicked the patient\u2019s gum with a sharp instrument. This allowed <em>Streptococcus<\/em>, a bacterium normally present in the mouth, to gain access to the blood. As a result, the patient developed bacterial endocarditis (an infection of the heart). Which type of disease is this?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>iatrogenic<\/li>\n<li>nosocomial<\/li>\n<li>vectors<\/li>\n<li>zoonotic<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q954408\">Show Answer<\/span><\/p>\n<div id=\"q954408\" class=\"hidden-answer\" style=\"display: none\">Answer a. This is an iatrogenic disease.<\/div>\n<\/div>\n<p>Which period is the stage of disease during which the patient begins to present general signs and symptoms?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>convalescence<\/li>\n<li>incubation<\/li>\n<li>illness<\/li>\n<li>prodromal<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q164648\">Show Answer<\/span><\/p>\n<div id=\"q164648\" class=\"hidden-answer\" style=\"display: none\">Answer d. The patient begins to present general signs and symptoms during the\u00a0prodromal stage.\u00a0<\/div>\n<\/div>\n<p>A communicable disease that can be easily transmitted from person to person is which type of disease?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>contagious<\/li>\n<li>iatrogenic<\/li>\n<li>acute<\/li>\n<li>nosocomial<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q395546\">Show Answer<\/span><\/p>\n<div id=\"q395546\" class=\"hidden-answer\" style=\"display: none\">Answer a. This is a contagious disease.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Fill in the Blank<\/h3>\n<p>A difference between an acute disease and chronic disease is that chronic diseases have an extended period of __________.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q25370\">Show Answer<\/span><\/p>\n<div id=\"q25370\" class=\"hidden-answer\" style=\"display: none\">A difference between an acute disease and chronic disease is that chronic diseases have an extended period of <strong>illness<\/strong>.<\/div>\n<\/div>\n<p>A person steps on a rusty nail and develops tetanus. In this case, the person has acquired a(n) __________ disease.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q60821\">Show Answer<\/span><\/p>\n<div id=\"q60821\" class=\"hidden-answer\" style=\"display: none\">A person steps on a rusty nail and develops tetanus. In this case, the person has acquired a\u00a0<strong>noncommunicable<\/strong> disease.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ol>\n<li>Brian goes to the hospital after not feeling well for a week. He has a fever of 38 \u00b0C (100.4 \u00b0F) and complains of nausea and a constant migraine. Distinguish between the signs and symptoms of disease in Brian\u2019s case.<\/li>\n<li>Two periods of acute disease are the periods of illness and period of decline.\n<ol style=\"list-style-type: lower-alpha;\">\n<li>In what way are both of these periods similar?<\/li>\n<li>In terms of quantity of pathogen, in what way are these periods different?<\/li>\n<li>What initiates the period of decline?<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Critical Thinking<\/h3>\n<p>In July 2015, a report<a class=\"footnote\" title=\"C. Owens. &quot;P. aeruginosa survives in sinks 10 years after hospital outbreak.&quot; 2015. http:\/\/www.healio.com\/infectious-disease\/nosocomial-infections\/news\/online\/%7B5afba909-56d9-48cc-a9b0-ffe4568161e8%7D\/p-aeruginosa-survives-in-sinks-10-years-after-hospital-outbreak\" id=\"return-footnote-686-4\" href=\"#footnote-686-4\" aria-label=\"Footnote 4\"><sup class=\"footnote\">[4]<\/sup><\/a> was released indicating the gram-negative bacterium <em>Pseudomonas aeruginosa<\/em> was found on hospital sinks 10 years after the initial outbreak in a neonatal intensive care unit. <em>P. aeruginosa<\/em> usually causes localized ear and eye infections but can cause pneumonia or septicemia in vulnerable individuals like newborn babies. Explain how the current discovery of the presence of this reported <em>P. aeruginosa<\/em> could lead to a recurrence of nosocomial disease.<\/p>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-686\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>OpenStax Microbiology. <strong>Provided by<\/strong>: OpenStax CNX. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2\">http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Download for free at http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section><hr class=\"before-footnotes clear\" \/><div class=\"footnotes\"><ol><li id=\"footnote-686-1\">F. Savino et al. \"Pain Assessment in Children Undergoing Venipuncture: The Wong\u2013Baker Faces Scale Versus Skin Conductance Fluctuations.\" <em>PeerJ<\/em> 1 (2013):e37; https:\/\/peerj.com\/articles\/37\/ <a href=\"#return-footnote-686-1\" class=\"return-footnote\" aria-label=\"Return to footnote 1\">&crarr;<\/a><\/li><li id=\"footnote-686-2\">J.G. Kusters et al. Pathogenesis of <em>Helicobacter pylori<\/em> Infection. <em>Clinical Microbiology Reviews<\/em> 19 no. 3 (2006):449\u2013490. <a href=\"#return-footnote-686-2\" class=\"return-footnote\" aria-label=\"Return to footnote 2\">&crarr;<\/a><\/li><li id=\"footnote-686-3\">N.R. Salama et al. \"Life in the Human Stomach: Persistence Strategies of the Bacterial Pathogen <em>Helicobacter pylori<\/em>.\" <em>Nature Reviews Microbiology<\/em> 11 (2013):385\u2013399. <a href=\"#return-footnote-686-3\" class=\"return-footnote\" aria-label=\"Return to footnote 3\">&crarr;<\/a><\/li><li id=\"footnote-686-4\">C. Owens. \"<em>P. aeruginosa<\/em> survives in sinks 10 years after hospital outbreak.\" 2015. http:\/\/www.healio.com\/infectious-disease\/nosocomial-infections\/news\/online\/%7B5afba909-56d9-48cc-a9b0-ffe4568161e8%7D\/p-aeruginosa-survives-in-sinks-10-years-after-hospital-outbreak <a href=\"#return-footnote-686-4\" class=\"return-footnote\" aria-label=\"Return to footnote 4\">&crarr;<\/a><\/li><\/ol><\/div>","protected":false},"author":17,"menu_order":2,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"OpenStax Microbiology\",\"author\":\"\",\"organization\":\"OpenStax CNX\",\"url\":\"http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-686","chapter","type-chapter","status-publish","hentry"],"part":680,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/chapters\/686","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":3,"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/chapters\/686\/revisions"}],"predecessor-version":[{"id":1635,"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/chapters\/686\/revisions\/1635"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/parts\/680"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/chapters\/686\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/wp\/v2\/media?parent=686"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/chapter-type?post=686"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/wp\/v2\/contributor?post=686"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/wp\/v2\/license?post=686"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}