What Do Epidemiologists Do During a Disease Outbreak?

What Do Epidemiologists Do?

Epidemiology is a foundational component of public health that examines how diseases, injuries and other health conditions affect populations. Clinicians generally diagnose and treat individual patients. Epidemiologists review numerous cases to determine who is affected, where illnesses are occurring and which exposures or conditions may be contributing to them.

They may use information from patient interviews, medical records, laboratory tests, surveillance databases, environmental assessments and geographic data. And although infectious disease epidemiology becomes particularly visible during an outbreak, epidemiologists also study chronic diseases, environmental hazards, injuries, maternal and child health and many other population health concerns.

According to Dr. Frazier Beatty, PhD, MPH, director of Regis College’s Master of Public Health program, the profession combines scientific analysis with the curiosity needed to reconstruct how a health threat developed.

“It’s really like investigation or detective-type work,” Beatty says. “They do the detective-type work, and then they take those exposures and track them back to the source. That’s what an epidemiologist does on a regular basis—the tracking and trying to find out where it started.”

How Do Epidemiologists Investigate a Disease Outbreak?

Although public health agencies follow established outbreak-investigation methods, the process is not always perfectly linear. Investigators may complete several steps simultaneously, revise their initial theories or recommend protective measures before every question has been answered.

1. Detect Unusual Illness Patterns

Possible outbreaks are often first detected via reports from clinicians, laboratories and local health departments. Epidemiologists compare the number and characteristics of current cases with what would ordinarily be expected within that population, location and time period.

That information typically begins at the community level.

“Generally, what happens is there’s a problem with somebody’s food, and the local public health department usually gets the information,” Beatty says. “They interview the people. That information is taken by the local health department, and they report their information, their data and their communication up to the state health department.”

When an investigation crosses state lines or involves a regulated product, national agencies such as the Centers for Disease Control and Prevention or Food and Drug Administration may become involved.

2. Define and Identify Cases

Investigators are looking for consistent criteria to decide which illnesses may be associated with an outbreak. Epidemiologists consider symptoms, laboratory findings, where and when an illness occurred and other characteristics of affected individuals.

Public health professionals may interview patients about foods they ate, restaurants they visited, stores where they shopped or recent travel to determine where the exposure may have occurred. These conversations help determine whether seemingly unrelated illnesses share an important connection.

3. Study Cases by Person, Place and Time

Investigators organize the available information to understand who is becoming ill, where cases are occurring and when symptoms began. Mapping tools and geographic information systems help professionals identify clusters that would be difficult to recognize from isolated reports.

“The first thing that they’re doing is trying to figure out who’s becoming ill,” Beatty says. “They have a geographic information system (GIS) tracking. They have ZIP code tracking. They start to track the information of who’s becoming ill and then where the cases are occurring.”

A pattern may gradually emerge as information from different hospitals, laboratories and health departments is brought together.

4. Trace Exposures and Develop Hypotheses

Once investigators identify commonalities, they begin testing potential explanations. In a foodborne outbreak, this may mean tracing a product backward through restaurants, retailers, distributors, processing facilities and farms to determine where the problem may have originated.

“They try to trace it back to the source,” Beatty says. “It could have come from the processing place where they processed the vegetables on the farm, or it could have gotten to the warehouse and somebody could have made a mistake in the warehouse where they didn’t store it properly. They go back and track it.”

Epidemiologists may compare the experiences of people who became ill with those of people who did not. They also coordinate their findings with laboratory scientists and environmental health professionals.

Public health professionals also understand that theories can change as new information emerges. That uncertainty is not necessarily evidence that an investigation has failed. It reflects a scientific process in which conclusions must continually be tested against the available evidence.

5. Recommend and Evaluate Control Measures

Epidemiologists communicate their findings to health officials and other decision-makers. Depending on the threat, public health measures could include removing a product, issuing a recall, alerting healthcare providers, correcting an unsafe process or communicating precautions to the public.

On some occasions, agencies may need to act before investigators have conclusively answered every question, as awaiting perfect information may allow more illnesses to occur. However, moving too quickly based on weak evidence can lead to the implementation of unnecessary or ineffective measures.

That’s why continued disease surveillance is essential in helping officials assess whether their response is working.

Why Outbreak Response Requires an Entire Public Health System

An epidemiologist may play a central role in identifying patterns and tracing exposures, but no individual professional can manage an outbreak alone.

A successful response can involve healthcare providers, public health laboratories, environmental inspectors, biostatisticians, informatics professionals, health educators, communications teams, policymakers and agency administrators. Foodborne illness investigations can also require cooperation from farms, processors, distributors, restaurants and retailers.

“Public health is a vast and broad area that most people misunderstand,” Beatty says. “It’s a collaborative effort. Everybody works in tandem… You can’t just have the epidemiologists over here and the biostatisticians over here and environmental health people over here. Everybody works together to keep the public safe.”

This collaboration is one reason public health careers are so interdisciplinary. Epidemiologists need dependable reporting systems, laboratory capacity, trained personnel, communication channels and organizational support. When data is incomplete or systems cannot exchange information efficiently, it becomes harder to recognize a threat and respond quickly.

Public Health Work Starts Before an Outbreak

Outbreaks often create the impression that public health professionals are activated only after an emergency begins. In reality, the ability to recognize a crisis depends on extensive work already underway.

Epidemiologists and their partners continually conduct disease surveillance, inspect food and environmental conditions, analyze laboratory samples, monitor community health trends and prepare emergency communication plans.

“Here is where I think the public misunderstands: They think it all starts when the crisis starts,” Beatty says. “Public health work does not begin when a crisis becomes visible. Epidemiologists are already monitoring health data, while environmental health and food-safety professionals are conducting inspections and identifying possible risks. That work is happening all the time.”

A restaurant’s inspection grade, a laboratory’s routine testing process or a clinician’s disease report may seem disconnected from outbreak response. Together, however, these activities create the system that allows an unusual pattern to be detected.

How are Technology and AI Changing Outbreak Investigations?

Epidemiologists increasingly work with large volumes of information spread across different databases and organizations. Artificial intelligence tools may help professionals connect those data sources, process reports and identify patterns more efficiently.

Beatty points to disease detection as an area where AI can be most helpful. Because data during an outbreak is likely coming from numerous systems all at once, AI tools can be used to bring that information together quickly, speeding up the time in which public health officials respond to an event.

For example, during a foodborne illness outbreak, information is collected from numerous sources, from hospitals to food-distribution centers. AI-assisted systems can quickly compare those sources and identify patterns, such as whether patients in several locations reported eating the same product, if their illnesses began within a similar time frame and or if the product passed through a common distributor.

Public health professionals still need to verify the pattern and investigate the source, but AI can surface those connections much faster than teams manually reviewing each report and database one at a time.

Yet, while it can dramatically speed up processes, AI cannot eliminate the need for public health expertise.

“People sometimes say that AI is replacing professionals, but that is not really the case,” Beatty says. “Trained people still have to guide the technology, ask the right questions, evaluate the information it produces, and determine whether the results make scientific sense.”

Public health professionals must still assess data quality, recognize misleading relationships, interpret findings and apply ethical and scientific judgment. So while technology can accelerate parts of an investigation, it still requires trained individuals to responsibly determine what the evidence means and how it should inform action.

What Skills Do You Need in Public Health—and How a Master's Education Can Help

Responses to an outbreak can help  illustrate why professionals in the public health sphere need a combination of analytical and interpersonal abilities. Relevant public health skills include:

• Research
• Data interpretation
• Systems thinking
• Communication
• Collaboration
• Problem-solving

Integrity and compassion are equally important as public health decisions affect real communities, often when people are frightened or reliable information is still emerging.

That’s one of the reasons why epidemiologists and public health officials in general often come from varied backgrounds.

“Anyone who wants to come into public health and has a heart of service can come in and do a wonderful job,” Beatty says. “There’s no specific background. Some would say, ‘I have a background in health or something health-related,’ but that’s not how I feel about it.”

A scientist may bring laboratory knowledge, while someone from education, communications or marketing may understand how to translate complicated guidance for the public. What matters is developing technical competencies that then can be  used in service of others.

How Can an MPH Prepare You to Make a Public Health Impact?

Graduate education is one pathway for developing the advanced analytical, research and leadership skills used in many public health careers. An MPH, such as Regis’ Master of Public Health, provides a broad foundation in epidemiological methods, biostatistics, environmental health, social and behavioral sciences, health ethics and law and health administration.

Students in Regis’ program can select an Epidemiology concentration focused on disease patterns, causes, prevention, surveillance and health investigations. The curriculum includes an Infectious Disease Epidemiology course covering outbreak investigations, disease surveillance and common research methods.

Through an applied capstone or public health practicum, students can also use what they have learned to address a real population health challenge.

This preparation can help graduates pursue a field in which employment of epidemiologists is projected to grow 16% between 2024 and 2034, according to the U.S. Bureau of Labor Statistics—much faster than the national average.

Prepare to Help Protect the Public

A public warning or product recall represents only the most visible portion of an outbreak response. Behind it are epidemiologists connecting cases, interviewing patients, studying patterns, evaluating possible sources and working with partners to protect communities.

Recent outbreak investigations help bring that role into focus. They also demonstrate why public health needs skilled professionals and strong systems well before the next threat appears.

Regis College’s MPH program can help you build the analytical knowledge, practical experience and community-centered perspective needed to contribute.

Want to know more? Explore the Master of Public Health program or, if you have more questions, request more information and get the answers you’re looking for.