The epidemiological triad is a conceptual model that connects various factors of a health problem, and leads to implementing intervention of the problem. According to the Centers for Disease Control, “Epidemiologic Triangle is a model that scientists have developed for studying health problems” (“Understanding the Epidemiologic Triangle through Infectious Disease”). The model identifies the susceptible host (person at risk of disease), a disease agent (proximate cause), and environmental conditions for the interaction between the host and agent (“Principles of Epidemiology in Public Health Practice, 2012). The purpose of the model is to identify the correlation between each of the factors of host, agent, and environment, and their ultimate connection with the infectious disease. The concept of the epidemiological triad is observed in many other health theories that are ideally conceptualizing the factors of infectious disease. Theories that follow the idea of the triad model include Theory of Reasoned Action and Theory of Planned Behavior, The Health Belief Model, as well as the Precaution adoption process model.

The Theory of the Reasoned Action and the Theory of Planned Behavior are models that “focus[es] on theoretical construct[s] that [are] concerned with the individual motivational factors as determinants of the likelihoods of performing specific behaviors.” (Glanz, Rimer, and Viswanath, 2015). The TRA and TPB assume a causal chain that link socio-behavioral beliefs, normative beliefs, and control beliefs in the environment to behavioral intentions and behaviors via attitude, subjective norms, and perceived control of the host for management of the agent that is the main cause for the disease.

Comparatively, according to the Resource Center for Adolescent Pregnancy Prevention, The Health Belief Model is a framework for motivating people to take positive health actions that uses the desire to “avoid a negative health consequence” as the prime motivation (ReCAPP: Theories & Approaches: Health Belief Model (HBM)). The Health Belief Model revolves around the idea of the three main factors just like the triad model. This HBM consists of individual perception and psychological states of a host, modifying factors such as demographic and socio-psychological variables in the environment, and likelihood of action of the host, which is a reflection of epidemiological triad model.

Additionally, according to Center for Health Behavior Research of the University of Pennsylvania, the PAPM attempts to explain how a person comes to decisions to take action and how he or she translates that decision into action (Health and Education, 2013). The PAPM describes a set of categories (stages), defined in terms of psychological processes within individuals. All stages are defined in terms of mental states, rather than factors external to the person, such as current or past behaviors. The PAPM mainly focuses on the physiological processes within individuals. By considering the physiological state of a person, this model can visualize the state of environment that they are currently in and also demonstrate insight of the individual’s knowledge about the exposure of the agent. In connection to these models, the chapter discusses some communicable diseases in order to have a deeper understanding of the theories.