Epidemiology: Definition, Components, Scope, History

Epidemiology is a branch of medical science that studies the determinants, and occurrence of diseases in a defined population along with their distribution.

It is derived from the Greek language composed of ‘epi’ meaning upon, ‘demos’ meaning people, and ‘logos’ meaning study. It refers to the study of all the factors that control or influence the presence or absence of a disease in a community. In broader terms, it is a fundamental science of public health used to prevent and control health problems and diseases in the human population, chiefly through quantitative methods.

Epidemiology
Epidemiology

Although considered a relatively new discipline, the field of epidemiology is vast concerning its interrelation with biostatistics, health, and biomedical sciences including pathology, microbiology physiology, and social sciences including anthropology, sociology, and psychology. The principles of epidemiology are based on producing quantitative evidence for health-related phenomena (eg: mortality, morbidity), thereby contributing to the betterment of clinical and community medicine. 

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Components of Epidemiology

Carrier: In epidemiology, a carrier is defined as an individual that harbors infectious organisms or pathogens but has no visible effects.

Population: A defined group of individuals is known as a population. A certain population may be a country, a state, a city, a community, or a neighborhood depending on the occurrence, determinants, distribution, and transmission of disease and related risks.

Determinants: The factors, elements, or events that bring about a change in health. It refers to the root causes contributing to a disease’s risk, focusing more on the cause and effect. For example, biological agents such as bacteria when associated with other pathogens or chemical agents act as carcinogens.

Distribution: The frequency at which a disease occurs along with the patterns or trends of its occurrence is known as distribution. The distribution of a disease depends on the underlying characteristics of a population. For example, in 2006, the death rates of African Americans suffering from coronary heart disease (CHD) and stroke were higher in comparison to American Indians, Alaskan natives, and Asian/Pacific islanders. 

Morbidity and Mortality: Morbidity simply refers to illness or incidence of a disease and mortality refers to death. It is considered that epidemiology centers on these two terms. 

Scope of Epidemiology

With the evolution of population science in the past centuries, the scope of epidemiology has broadened with time. The curiosity, speculation, and confusion around epidemiology, its areas of application, and proper methods of investigation have widened the spectrum of possibilities and opportunities related to it.

The various scopes of epidemiology are outlined below:

  • As it studies the occurrence and determinants of a disease (infectious and non-infectious) in a population, it identifies and describes the factors responsible for causing the health condition along with its underlying characteristics.
  • It determines the frequency at which the diseases occur, estimates the cases of diseases in different subgroups, and identifies the patterns or trends of their occurrence along with the modes of transmission.
  • It supports the major activities of clinical medicine such as diagnostics, etiognosis (knowing about the cause of a disease), intervention, and prognosis (understanding the future course of the disease) by providing proper foundation and methodologies.
  • It supports various aspects of community medicine through screening, surveillance, and health profiling employing surveys, disease modeling, and outbreak investigation.
  • The identification of factors that increase the risk of diseases or adverse health events, aids in community intervention studies and prevention research to monitor, plan, and implement public health intervention and services, and healthcare resources allocation.
  • The epidemiologic approach is used to control the distribution of disease by preventing the occurrence of new cases, eliminating existing cases, and extending the lifespan of individuals already affected by the disease.
  • Based on the epidemiological findings, utilization of health services and resources, and analysis of effectiveness, it evaluates the health status of a certain population and suggests new plans and strategies to prevent or control health issues. 

History and Evolution of Epidemiology

The history of epidemiology and its evolution has been slow and unsteady, contributed by many key figures who observed, understood, and explained illness, injuries, infections, and death from a scientific viewpoint. The origin of Epidemiology dates back to 20 centuries ago when Hippocrates, known as the father of Medicine observed that the occurrence of the disease was influenced by environmental factors. From the first known epidemiologist Hippocrates, who explained the occurrence of diseases from a rational perspective to John Graunt in the 16th century who described the occurrence of disease and death using systematic methods to Thomas Syndemham who approached the occurrence of diseases from an observational and analytical viewpoint, the historical developments of epidemiology have progressed significantly. However, it was in the 19th century that epidemiology emerged as the fundamental science of public health action with important contributions and major achievements. The following timeline briefly highlights some notable historical developments in epidemiology: 

17th Century: In the 1700s, a Scottish Naval surgeon, James Lind observed that a significant number of armies died of diseases than wars. With the identification of the symptoms, Lind noticed that sailors on long voyages suffered from Scurvy, a disease marked by bleeding gums, skin, and weakness. He carried out an experimental survey with 12 sick sailors with the same extent of disease, divided them into pairs of two, and provided them with different dietary interventions. It was observed that oranges and limes when included in the diet worked as the best remedies for scurvy. 

18th Century: Edward Jenner, in the early 1800s, found that people who contracted cowpox did not contract smallpox. Through his observations and experiments in dairymaids, he found that cowpox was a shield against smallpox and later invented vaccination against smallpox. This intervention is considered a milestone in the history of epidemiology that led to the eradication of smallpox in the 19th century. Similarly, an English physician, John Snow renowned for his medical association with the royal family, studied Cholera epidemics. With the establishment of epidemiological methods, he carried out both descriptive and analytical investigative studies of the cholera outbreak in London. He took various parameters including mode of transmission, temperature, incubation time, water sources, climate, etc into consideration while conducting the experiments. 

19th Century: It was during this time that the distribution of disease in specified populations was measured to a larger extent. Based on the foundations laid in the past century, William Farr, a British physician contributed to the knowledge of statistics in England. He established a statistical tool used to classify the causes of deaths and record-keeping about a population. This marked the beginning of exploring statistical aspects of epidemiology. Many other notable names in the historical developments of epidemiology include Louis Pasteur, Ignaz Semmelweis, Robert Koch, Florence Nightingale, etc. who made notable contributions in this field.  

Role of Epidemiology in Public Health

Epidemiology, also known as population medicine has an interdisciplinary approach including biomedicine, statistics, microbiology, history, anthropology, transitional history, etc. However, various aspects of epidemiology intersect with public health as it is greatly concerned with communicable diseases, their occurrence, transmission, and prevention to improve the health status of population groups. Epidemiology is used as an essential tool in public health to improve health conditions and plan effective interventions, health programs, and preventive methods. Epidemiologists and public health workers go hand in hand to define and characterize the health of populations and their communities. 

References

  1. WEBB JR., James (2020). Historical epidemiology and global health history. História, Ciências, Saúde. 27, p.13-28.
  2. Liu, Z (2022). The Scope of Epidemiology. Epidemiol Sci.12(3) DOI: 10.4172/2327-4972.1000429
  3. Van den Broeck, J., Brestoff, J. R., & Baum, M. (2013). Definition and Scope of Epidemiology. Epidemiology: Principles and Practical Guidelines, 3-18. DOI:10.1007/978-94-007-5989-3_1 
  4. https://www.britannica.com/biography/Hans-Zinsser
  5. https://samples.jbpub.com/9781449665494/chapter1.pdf
  6. https://www.ncbi.nlm.nih.gov/books/NBK7993/
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  9. https://iris.who.int/bitstream/handle/10665/43541/9241547073_eng.pdf;jsessionid=2B2424FC212A065BA6FD784199995976?sequence=1
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About Author

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Dipika Shrestha

Dipika Shrestha is a BSc. Microbiology graduate from St. Xavier's College, Kathmandu. She has a strong grounding in academic research and writing. Over the years, through her involvement in research, she has developed an interest in Epidemiology, Antimicrobial Resistance (AMR), and Public Health. She is passionate about contributing to scientific advancements and leveraging her skills to drive impactful results to build a sustainable community.

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