Oct. 21 2020

What Is Epidemiology?

For many people, the COVID-19 pandemic was the first time they’ve been exposed to the idea of an uncontrolled disease—introducing phrases like “transmission,” “incubation period,” “contact tracing,” and “herd immunity” into the public vernacular. But for those in the field of epidemiology, these ideas are at the core of their careers, and a pandemic is exactly what they’ve been preparing for. Epidemiologists have historically performed vital work to protect and improve the health of populations, whether it is neighborhoods, cities, countries, or continents.

Epidemiologists are crucial in mapping and understanding the effects of the coronavirus, but their work extends beyond novel viruses and pandemics. So, what is this unique field? And how do epidemiologists approach issues in public health?

What is epidemiology?

Epidemiology is the foundation of public health and is defined as the study of the “distribution and determinants” of diseases or disorders within groups of people, and the development of knowledge on how to prevent and control them. Epidemiological research helps us understand not only who has a disorder or disease but why and how it was brought to this individual or region.

One of the earliest instances of modern epidemiology can be found during an 1854 cholera outbreak in London. Doctors believed the widespread illness must have been airborne, but Dr. John Snow, widely considered to be the father of epidemiology, employed a different kind of thinking. By carefully mapping the outbreak and analyzing those who were infected, Snow was able to link every cholera case to a single water pump at the intersection of Broad and Cambridge Streets (now Lexington Street) in London’s Soho neighborhood. The removal of the pump stopped the disease in its tracks—laying the basis of today’s epidemiological practices.

Today, epidemiologists use the insights gathered in their research to determine how illness within a population affects our society and systems on a larger scale, and in turn, provide recommendations for interventions, such as removing a fatal water pump.

As the novel coronavirus became widespread, epidemiologists around the world worked to control the spread. Our research spans work to better understand the virus and how it is transmitted; to project its spread and identify vulnerable communities; to develop diagnostic tests and therapies; and, to assess the U.S. and global health systems’ preparedness. See examples of our faculty's work with COVID.

Types of epidemiology

Epidemiology can cover a wide range of issues, from unintentional injuries to psychosocial stress. Here are a few areas in which Columbia Mailman faculty and students work:

  • Infectious Disease Epidemiology for Public Health 
    This type of epidemiology is at the forefront of today’s world—as epidemiologists work on the front lines to track and trace the spread of COVID-19. In this concentration, infectious disease epidemiologists work to detect pathogens or viruses, understand their development and spread, and devise effective interventions for their prevention and control.

  • Chronic Disease Epidemiology
    Chronic disease epidemiologists battle day-to-day chronic conditions such as cancers, diabetes, obesity, and more. Epidemiologists in this fieldwork to research the origins, treatment, and health outcomes of these diseases in the fight towards prevention.

  • Environmental Epidemiology
    Environmental epidemiology focuses on how an individual’s external factors affect health outcomes. This includes physical factors like pollution or housing, as well as social factors like stress and nutrition. Environmental epidemiologists work to understand how different environments may result in physical or neurological outcomes, ranging from psychiatric to cardiovascular disorders. 

  • Violence and Injury Epidemiology
    This epidemiological focus aims to address unintentional and intentional injuries across a lifespan. For example, epidemiologists in this field might focus their research on car accidents and work to identify the associated risk factors. Armed with extensive research, the goal of violence and injury epidemiology is to improve a population’s health by reducing the morbidity and mortality rate from unintentional and intentional injuries.

How epidemiologists track diseases

Epidemiology centers around the idea that disease and illness do not exist randomly or in a bubble. Epidemiologists conduct research to establish the factors that lead to public health issues, the appropriate responses, interventions, and solutions.

By using research—from the field and in the lab—and statistical analysis, epidemiologists can track disease and predict its future outcomes. In the case of COVID-19, this analysis requires heavy data surveillance, collection, and interpretation. 


Due to the scale and threat of the coronavirus pandemic, testing centers, and healthcare systems are required to report all related data, providing epidemiologists with a wealth of information upon which to base their studies. With this information, epidemiologists will track data including:

  • Number of Incidences (how many cases over time?)

  • Disease Prevalence (how many cases at a specific time?)

  • Number of Hospitalizations

  • Number of Cases Resulting in Death

Epidemiological Modeling

Using this data and more, epidemiologists create models that help predict the spread of the disease in the future—including where and when the spread may occur. They may also be able to discern the most vulnerable populations likely to contract a disease and provide recommendations for intervention. See examples of our faculty's work modeling COVID data.

Contact Tracing

In an attempt to stop the spread of disease and understand where it might go next, many public health workers use contact tracing to determine the connections of an infected person. See what some of our students have been doing: Students take the lead on the COVID-19 response.

Degrees in epidemiology

By achieving a degree in epidemiology, you are poised to work in places such as local health departments, nonprofits, government organizations, academia, the pharmaceutical industry, and more. 

With Columbia Public Health programs ranging from MPH, MS, DrPH, and PhD, students at all levels can gain the necessary knowledge to drive public health initiatives and conduct independent epidemiological research. Our graduates go on to work in roles at companies and organizations ranging in size, scope, and mission, such as:

  • Data and Informatics Analysts at medical technology firms, hospitals, and universities 

  • Research Scientists at statewide health departments 

  • Fellows at the Centers for Disease Control and Prevention (CDC) 

  • Clinical Trial Associates at international research laboratories

  • Research and Evaluation Manager at nonprofit organizations

Other areas of employment among our graduates include:

  • Consulting firms

  • Health insurance companies

  • Marketing and strategic communications firms

  • Pharmaceutical and biotechnology or medical device companies

The Department of Epidemiology at Columbia University Mailman School of Public Health is committed to producing world-class science with real-world impact while training the next generation of epidemiologists to improve the health and lives of communities around the world. Apply today or explore our overview book for more info.