Although epidemiology was initially designed to control and prevent epidemics of communicable disease, the model was later expanded to address the prevention of communicable and noncommunicable disease. By late 20th century, additional methods were developed to apply the model for chronic disease as well (CDC, 2012). According to National Center for Health Statistics, chronic diseases are diseases that lasts for 3 months or more and require ongoing medical attention. Treatments such as vaccinations and medications can help manage the disease but they cannot be cured. Chronic diseases such as diabetes, cancer, and heart disease are leading cause of death and disability in United States (CDC, 2018).

Source:https://www.researchgate.net/figure/Hypothesis-Testing-The-epidemiologic-triangle

The Epidemiological Triad of Chronic disease studies the distribution and the causal factors of the disease, which are then applied to the study of controlling and preventing the chronic health problem (CDC, 2012).

Application of Epidemiology Triad to Asthma:

In the United States, asthma is one of the most prevalent respiratory illnesses in both young and old, but predominantly in children. Asthma is a chronic lung condition that causes inflammation and narrowing of airway passage. Due to the swelling and constriction, the lungs receive less air, making it difficult to breathe and causes coughing, wheezing, chest tightness, etc. The Global Initiative for Asthma (GINA) indicated that asthma is a major disease affecting over 300 million people worldwide, but you can see it largely in minorities and school-aged children growing up in poor urban environments (Paul, 2017).

Agent

Agents are microbes that cause the disease. Disease causing microbes includes: bacteria, virus, fungi, and protozoa. Even though there are no known agents that causes atopic asthma, there are many that cause or trigger non-atopic asthma. Some of the agents that trigger non-atopic asthma are Chronic Mycoplasma pneumonia and Chlamydia pneumonia (Hong, 2012).

Host

As mentioned in the introduction, the host refers to the human capable of developing the disease. Some of the factors of hosts contributing to the prevalence of asthma are genetics, ethnicity and socioeconomic status, sex, and gender.

• Genetics:
  • Many studies conducted on families and twins have indicated that genetics play an important role in development of asthma and allergies (Paul, 2017)

• Sex and Gender:
  • Sex and gender also affect the prevalence of asthma. Males have higher chances of developing asthma till age 13-14. Studies have shown that females have higher chances of developing asthma during adolescence than during their young adulthood (Padmaja, et al., 2009).

• Lung Function:
  • Many studies have associated decreased airway calibre with development of asthma later in life. Decreased airway calibre has been associated with increased symptoms of wheezing and increased bronchial responsiveness, which increases the likelihood of developing asthma later in life (Padmaja, et al., 2009).

Environment

Environmental factors consist of everything outside the host, and they show how environmental exposure effects the disease. Environmental exposures that can cause or trigger asthma are: Ethnicity and socio-economic status, second-hand Smoking, and maternal smoking.

• Ethnicity and Socio-economic Status:
  • The number of asthma morbidity cases and more severe cases are usually higher in ethnic minorities and families from lower socio-economic status in the United States. Living in a poor-urban society, children usually don’t have the access to necessary equipment to improve their lungs. This include fewer nutrients, lack of sanitation, reduced exercise, and costs of hospitalization. Certain areas in U.S., specifically those below the poverty line, have a higher percentage of the disease, and are 3x more likely to be hospitalized than those who live in rich neighborhoods (NYC Department of Health, 2003).
• Second-Hand Smoking:
  • Another environmental factor that exacerbates asthma is second-hand smoke because tobacco is one of the most common and harmful triggers. Second-hand smoke from cigarettes contains over 7000 chemicals and about 70 that are carcinogenic (CDC, 2012). The smoke can trigger a child’s airways, which can lead to having frequent flare-ups, missing school days due to emergency visits, increasing medicine usage, and asthma that is harder to control even with medicine (Hong, 2012).
• Maternal Smoking:
  • One of the main environmental factor for development of asthma is maternal smoking. Studies have associated maternal smoking with early childhood wheezing and decreases in airway calibre which may evolve into asthma later in Life (Hong, 2012).

All three components of the epidemiological triad are linked in development of asthma.