PUB 540 History, Principles, and Application of Epidemiology

PUB 540 History, Principles, and Application of Epidemiology

PUB 540 History, Principles, and Application of Epidemiology

Principles of Epidemiology

The prevalence of non-communicable diseases continues to rise, making them the leading cause of death globally. Similarly, infectious diseases have become more vicious, as demonstrated by the COVID-19 pandemic. At the same time, conditions such as malaria, Ebola, influenza, and HIV Aids, among others, persist in killing thousands of people yearly. Hence, the need to develop effective strategies for combating the ever-increasing health problems affecting global populations. The public health’s approach to understanding these diseases and creating a strategy for prevention is epidemiology. Epidemiology is a branch of biological sciences concerned with studying distributions and characteristics of populations, focusing on the health-related status of a given population (Forrest, 2019). For example, epidemiology studies a particular infectious disease such as tuberculosis within a specific population to understand its characteristics, including risk factors, distribution, and cause. The purpose of this paper is to discuss the history, principles, and importance of epidemiology and analyze the contributions of John Snow to the field of epidemiology.

The importance of epidemiology in public health is to understand disease characteristics by collecting data on the affected population and creating intervention strategies tailored to the needs of a specific population. For example, when the prevalence of obesity is high within a specific population, epidemiologists will employ data collection methods to understand the condition’s manifestations in that population, giving insights into what can be done to reduce the prevalence and prevent future occurrences (Friis & Sellers, 2021). In outbreaks such as the recent COVID-19, epidemiologists get to the bottom of the problem to analyze the possible causes, modes of transmission, and possible prevention strategies. Epidemiologists also combine the scientific knowledge from study with knowledge of patient and clinical judgment to create appropriate intervention and prevention strategies that enhance better health outcomes.

The principles of epidemiology include distribution, determinants, study, specific populations, and health-related states. Determinants are factors related to the cause of a disease or health-related events. The principle proposes that conditions do not arise randomly but originate from the accumulation of risk factors existing in an individual or population. The risk factors that can expose a group to health-related outcomes include demographic characteristics, genetics, immunologic make-up, environmental exposures, and behaviors. Thus, when investigating determinants, epidemiologists attempt to find out the “how” and “why” of disease occurrence (CDC, 2021). The second principle is distribution, which refers to the frequency and patterns of health-related conditions and diseases. Patterns are person, place, and time, while frequency is the number of events relative to the population size. The third principle is study, referring to the unbiased systematic collection of data, analysis, and interpretation (CDC, 2021). The fourth principle is specific populations is the concern about the collective health of a given affected by a disease or health-related condition. These principles are important for diagnosing the health of communities, leading to the development of intervention plans for the prevention of diseases and overall improvement in health outcomes of the community.

John Snow’s Contributions to Epidemiology

John Snow was an anesthesiologist who, in the mid-1800s, postulated that cholera was transmitted through water. However, the idea was rejected by the local authority and fellow researchers because the only acceptable explanation for the transmission of cholera was through air and pollution. Long before the invention of the microscope, Snow is famed for studying cholera outbreaks, contributing to the understanding of the cause of the disease and possible strategies for preventing reoccurrence (Willis, 2018). Snow identified contaminated water as the cause of the cholera outbreak in London. Between 1846 and 1860, a cholera pandemic occurred in various parts of the world. During this period, millions of people died in India, Russia, Africa, North America, and other places worldwide. The outbreak was the third cholera pandemic globally, which started in India, then crossed borders. One of the places severely affected by the outbreak was Broad Street in the City of Westminster, London. The outbreak affected 1300,149, with deaths reaching 652 people (CDC, 2021).

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Cholera outbreaks were common in the 19th century, with the first outbreak occurring in 1817. The third outbreak was more severe, with fatalities across the world. For example, in Great Britain alone, the pandemic killed 23,000 in a single year (Willis, 2018). The cholera pandemic was not associated with any season as it occurred subsequently for several years. Cholera outbreaks were common at the time because people had little knowledge of its cause; hence, it was hard to develop preventive strategies. It mainly affected people who lived in areas with contaminated places. For example, in Snow’s investigations in Soho London, he noted that the affected people were supplied water by the Lambeth, Southwark, and Vauxhall companies (CDC, 2021). The mode of transmission was water; however, before Snow’s investigations, people believed that transmission occurred through bad air and pollution.

Snow, also known as the father of epidemiology, studied cholera mortality data and identified the districts most

PUB 540 History, Principles, and Application of Epidemiology
PUB 540 History, Principles, and Application of Epidemiology

affected by the outbreak. He also noted that these districts received water from two water companies. One of the techniques he used was mapping, through which he noted that a cluster of cases occurred among people who lived near a particular water pump (CDC, 2021). The second technique Snow used was the characterization of cases and investigation of the population at risk by place, time, and person. This approach led him to develop a hypothesis about the possible cause of the cholera outbreak. To test the hypothesis, he carried out a rigorous study on each household affected by cholera to compare data and approved the hypothesis. His discovery prompted the health officials to remove the pump handle, subsequently reducing the rates of cholera infections. The discovery contributed to the control of the cholera pandemic worldwide.

Subspecialties in Epidemiology

The three main subspecialties of epidemiology are neuroepidemiology, pharmacoepidemiology, and social epidemiology. Neuroepidemiology studies characteristics of diseases that affect the central nervous system. The study investigates the occurrence, distribution, frequency, and determinants of disease. The second subspecialty, pharmacoepidemiology, is an epidemiological branch dealing with the study of the efficacy and safety of medications. The subspecialty analyzes the use of medications to estimate the beneficial effects for a large population, as well as potential side effects. The third subspecialty of epidemiology is social epidemiology, which examines the social-structural factors related to health outcomes (Roux, 2022). For example, the study looks at the distribution of resources in the society, which is often unequal, leading to different socio-economic outcomes. These are reflected in the health and disease outcomes of populations. For example, the social determinants of health are factors that reflect on health outcomes of communities.


Epidemiology is the basis of public health, providing a path to study and understand diseases and other health-related conditions among populations. The principles of epidemiology are distribution, determinants, study, and specified population. One of the pioneer contributors to epidemiology is John Snow, who studied the distribution and determinants of cholera to identify water as the main source of transmission. Snow used mapping, classification, and characterization of populations, hypothesis development, and rigorous study based on the hypothesis. These concepts are still used in epidemiological studies to date. Snow’s discovery contributed to the control of the cholera pandemic in the mid-1880s and the prevention of the disease. Finally, the three subspecialties of epidemiology are neuroepidemiology, pharmacoepidemiology, and social epidemiology.



CDC. (2021, May 18). Introduction to Epidemiology: Definition of Epidemiology. Retrieved from CDC:

CDC. (2021, May 18). Introduction to Epidemiology: Historical Evolution of Epidemiology. Retrieved from CDC:,cause%20of%20disease%20and%20to

Forrest, K. Y. (2019). Epidemiology. Magill’s Medical Guide, Salem Press.

Friis, R. H., & Sellers, T. A. (2021). Epidemiology for public health practice (6th ed.). Jones and Bartlett Learning.

Roux, A. V. (2022). Social Epidemiology: Past, Present, and Future. Annual Review of Public Health, 43:79-98.

Willis, M. (2018). John Snow and the Birth of Epidemiology. JSTOR.