The History and Key Components of Epidemiology

John Snow, the father of epidemiology, as experts suggest it, gave a path to the development of modern epidemiology as a scientific discipline and improved public health for medical professionals in an epidemiology course. It should be noted that “epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems” (Centers for Disease Control and Prevention, 2012, para. 8). This paper will further discuss the critical components of epidemiology and how they relate to Snow’s work and contributions.

The main epidemiologic approaches rely on precise observation of the situation and the application of relevant group’s comparison to evaluate whether what was noticed, including the number of illness cases in a specific region during a particular time or the frequency of exposure among persons with disease, is different from what is expected and evaluated as usual (Frérot et al., 2018). The distribution in the definition of epidemiology as a discipline refers to the frequency and pattern of health events happening in a specific population.

Frequency defines and estimates the number of disease cases that occurred and the ratio of this number to the population’s size (Frérot et al., 2018). The pattern defines the occurrence of epidemiologic cases by time, place, and person, investigating time patterns and landmarks, geographic variation, and demographic factors, such as age, sex, and others (Centers for Disease Control and Prevention, 2012). Distribution relates to the descriptive epidemiology direction in comparison to analytical epidemiology that includes determinants of the disease.

Determinants of epidemic illness cover causes and agents of the disease, risk factors (exposure to specific sources), transmission methods, answering questions of why and how. Researchers assume that epidemic diseases do not happen randomly in a population but occur when risk factors intersect with causes in a person. Determinants evaluate whether groups with a different disease frequency vary in their demographic, genetic, or immunologic features (Centers for Disease Control and Prevention, 2012). Finally, epidemiology includes the application or control of health problems that prevent the disease in a community or get control over it. However, it does not include the actual treatment and health interventions in people, which refer to the health care providers’ direction.

John Snow as the father of epidemiology, triggered the development of definitions of frequency, distribution, determinants, and control of disease described above due to his outstanding work during the cholera epidemic in London in 1854 (Fine et al., 2013). Researchers could not agree on the common cause of cholera, which led to tens of thousands of deaths in England. Snow decided to compare the frequency and death rates of previous and the current outbreak of the disease in 1854 and found that the cause of transmission was contaminated water (Chartered Institute of Environmental Health, n.d.). Snow used both the descriptive and analytical epidemiology to determine the source of cholera in a specific area of Soho in London by creating a spot map and asking authorities to stop the Broad Street source’s water supply.

A detailed study of the spread of cases in London with the help of innovative mapping at the time allowed John Snow to assume a waterway of cholera transmission, and not air (miasma), as previously thought (Fine et al., 2013). The study of John Snow served as an impetus for the development of epidemiology and the improvement of water supply and sewerage systems and contributed to the public health enhancement. Snow’s decision to put cholera cases on a geographical grid and compare disease occurrence tight to household water sources triggered the rapid development of the epidemiological knowledge as we know it today.


Centers for Disease Control and Prevention. (2012). Lesson 1: Introduction to epidemiology. Web.

Chartered Institute of Environmental Health. (n.d.). Dr John Snow, Physician. Web.

Fine, P., Victora, C. G., Rothman, K. J., Moore, P. S., Chang, Y., Curtis, V., Heymann, D. L., Slutkin, G., May, R. M., Patel, V., Roberts, I., Wortley, R., Torgerson, C., & Deaton, A. (2013). John Snow’s legacy: epidemiology without borders. Lancet (London, England), 381(9874), 1302–1311. Web.

Frérot, M., Lefebvre, A., Aho, S., Callier, P., Astruc, K., & Aho Glélé, L. S. (2018). What is epidemiology? Changing definitions of epidemiology 1978-2017. PloS one, 13(12), e0208442. Web.

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