The epidemiologic triad describes disease as a result of the relationship among a susceptible host, an external agent, and an environment that brings the host and agent together. Epidemiology is the scientific study of the distribution and determinants of diseases and health outcomes to improve the health and safety of populations by establishing causal factors for health issues.

By identifying causes and risk factors of disease development, public health nurses can intervene early to reduce morbidity and mortality from the disease. Epidemiology provides the opportunity to develop an evidence-based foundation for prevention programs

epidemiology — scientific study of the distribution and determinants of diseases and health outcomes in populations. agent — something physical, chemical, nutritional, psychosocial, or biologic that can cause a health issue; must be present for a disease to occur. host — an individual, a family, a group of high-risk individuals, or a community within the context of the epidemiological triad. morbidity — having a disease, illness, or medical condition; includes disease, injury, and disability.