What is Epidemiology?

Researchers have traced back epidemiology to the Age of Pericles in the 5th Century B.C. The term epidemiology is derived from the Greek word “epi” which means on or upon, “demos” which means people, and “logos” which means the study of. Therefore, it is the method of studying the reason behind the befall of a population.


Epidemiology. Image Credit: MarcoVector/Shutterstock.com

Epidemiology helps to determine the cause of a disease, its frequency or pattern of transmission, and also the extent of risk of the disease within a community/ school/ neighborhood/ nation/ world. This study also involves finding means to control the spread of diseases.

The COVID-19 pandemic has made many people aware of certain terms such as uncontrolled disease, transmission, herd immunity, etc. Epidemiologists deal with past, present, and future pandemics. In the current COVID-19 pandemic situation, epidemiologists have played a vital role in mapping and understanding how coronavirus affects the population. Many a time, epidemiology is regarded as the basic science of public health.

Epidemiology is a data-driven study that depends on a systematic and unbiased method of data collection and subsequently, on the analysis, and interpretation of this data. This study is based on developing and testing hypotheses and also includes biostatistics and informatics, with economic, biological, social, and health-related behavioral sciences.

Implementation of modern epidemiology was traced back to 1854 during the cholera outbreak in London. Initially, physicians believed that cholera was an airborne disease. However, Dr. John Snow, who is also known as the Father of Epidemiology, contradicted the belief. He conducted a thorough analysis of the disease pattern by studying infected individuals. He successfully associated the onset of cholera with a single water pump in London’s Soho neighborhood. The removal of the water pump stopped the disease. This episode paved the way for modern epidemiological studies.

Types of Epidemiology

There are different types of epidemiology covering a wide range of issues, ranging from accidental injuries to psychosocial stress. Some of these are listed below:

Infectious Disease Epidemiology

This is the most common type of epidemiology which deals with infectious diseases. Currently, it is involved with tracking the spread of COVID-19. The main role of infectious disease epidemiologists is to determine the nature of pathogens or viruses. It also involves the understanding of the life cycle of these pathogens, transmission patterns, and also devising strategies required for their prevention and control.

Chronic Disease Epidemiology

Patients with chronic diseases such as cancer, diabetes, and obesity struggle each day to fight the disease. Epidemiologists specialized in dealing with chronic diseases research to find the origin of such diseases. They work towards finding effective treatments, and also towards developing measures to prevent the disease.

Environmental Epidemiology

Epidemiologists in this field study the effect of different physical (pollution) and social factors (nutrition and stress). The main work of environmental epidemiologists is to understand the effect of different environmental factors on the physical and neurological outcomes, which may range from psychiatric to cardiovascular disorders of an individual.

Violence and Injury Epidemiology

This type of epidemiology focuses on the intentional and unintentional injuries of an individual. It mainly involves the determination of the risks associated with incidents such as car accidents. Thereby, it aims to reduce morbidity and mortality rates from unintentional and intentional injuries.

How do Epidemiologists Track Diseases?

Epidemiologists conduct extensive research to establish the factors responsible for public health issues. They are also concerned with formulating appropriate strategies, interventions, and solutions to tackle the disease. In general, epidemiologists track diseases and predict their future outcomes by following a systematic approach. The first stage is the collection of data from testing centers and healthcare systems. This data helps to evaluate the number of patients admitted to hospitals, the number of cases, deaths, and the number of active cases at any given point in time.

By analyzing this data, epidemiologists provide a clear picture of the virulence of the virus and how it would affect the population. They also develop models that help predict the future trajectory of the disease, in terms of, where, when, and the intensity of the disease. These predictions help the vulnerable population to take necessary precautions and, thereby, minimizing the risk of contracting the disease.

Is Epidemiology a True Science?

Many scientists, in the 21st century, have questioned if epidemiology a “true” science. The emergence of such doubts among the scientific community is unexpected given the contribution of epidemiology in the past and the direct impact it has had on millions of lives.

Some scientists have commented that epidemiology identifies the factors, cause, source, and distribution of disease by assessing the political, social, and scientific factors. This group of scientists considers epidemiology to be a unique science because it can predict disease risk.

However, another group of scientists has criticized its dependence on observational data and claimed epidemiology as a form of journalism rather than true science. Researchers have explained that epidemiology is sometimes trivialized because it is based on variables that are complex to quantify, e.g., human behaviors and interactions.

Epidemiological research has provided tangible results that has saved millions of lives from both communicable and non-communicable diseases via preventative programs. Even the Centre for Disease Control (CDC) credits medical epidemiologists. It states that owing to the contributions of epidemiologists, in the United States, 25 years could be added to the average life expectancy of people, since 1947.

Additionally, epidemiology plays a critical role in understanding the impact of climate change on disease incidence, e.g., the effect of temperature, humidity, and seasonal variations on infectious disease dynamics. It also correlates these environmental conditions with vector ranges that would rapidly spread an infection.


  • Epidemiology is a science of high importance. (2018). Nature Communication, 9, 1703. https://doi.org/10.1038/s41467-018-04243-3
  • Centers for Disease Control and Prevention. Principles of epidemiology in public health practice, 3rd Edition, An Introduction to Applied Epidemiology and Biostatistics. Available at: https://www.cdc.gov/csels/dsepd/ss1978/index.html
  • Last, J.M. (2001). Dictionary of epidemiology. 4th ed. New York: Oxford University Press; pp. 61
  • Cates, W. (1982). Epidemiology: Applying principles to clinical practice. Contemp Ob/Gyn, 20, pp.147–61.
  • Greenwood M. (1935). Epidemics and crowd-diseases: an introduction to the study of epidemiology, Oxford University Press.
  • Columbia Mailman School for Public Health. What is Epidemiology? Available at: www.publichealth.columbia.edu/public-health-now/news/what-epidemiology

Further Reading

Last Updated: Jul 5, 2021

Dr. Priyom Bose

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.


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