What Is Epidemiology? How MPH Students Use It to Track and Prevent Disease
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Epidemiology is the branch of public health science that investigates why diseases occur, who they affect and how to stop them from spreading. It is the discipline that answers one of the most fundamental questions in medicine: why does illness appear in some communities and not others?
For anyone considering a career in public health, understanding epidemiology is essential, and enrolling in Adelphi University’s online Master of Public Health (MPH) program is one of the most direct ways to build that expertise at an advanced level. Epidemiology informs many public health responses, from contact tracing during infectious outbreaks to identifying risk factors behind chronic conditions like heart disease and diabetes. Epidemiologists supply the evidence that guides many public health decisions.
What Is Epidemiology?
Epidemiology is the scientific study of how diseases and health conditions are distributed across populations, what causes them and how they can be controlled. The word itself comes from the Greek words for “upon” (epi), “people” (demos) and “study” (logos) — literally, the study of what falls upon people. Where a physician focuses on diagnosing and treating individual patients, an epidemiologist zooms out to examine patterns across entire communities, countries or the world.
According to the U.S. Bureau of Labor Statistics (BLS), epidemiologists are public health workers who investigate patterns and causes of disease and injury, with the goal of reducing the risk and occurrence of negative health outcomes through research, community education and health policy. The field blends biology, statistics and social science into a uniquely powerful toolkit, one capable of connecting seemingly unrelated data points into actionable public health insight and response.
How Epidemiologists Study Disease
Epidemiologists rarely work from a single data source. Their investigations begin with surveillance — the ongoing, systematic collection of health data to detect changes in disease rates. When a change is detected, whether a sudden spike in hospital admissions or an unusual cluster of illness, epidemiologists move into active investigation, collecting information through interviews, surveys, laboratory samples and medical records, then applying statistical methods to identify patterns.
According to the Centers for Disease Control and Prevention’s (CDC’s) Epidemic Intelligence Service (EIS), the collection, analysis and interpretation of data for evidence-based public health action is what distinguishes epidemiology from other health sciences. EIS, established in 1951, has trained more than 4,000 disease detectives who have deployed this method to respond to health emergencies worldwide.
Key Concepts: Incidence, Prevalence and Risk Factors
Three concepts anchor epidemiological thinking and appear throughout every MPH curriculum: incidence, prevalence and risk factors. Understanding each, and how they interact, is foundational to interpreting any population health data.
Incidence
Incidence refers to the number of new cases of a disease that develop in a specific population over a specific period of time. It measures how quickly a disease is spreading.
Prevalence
Prevalence measures the total number of existing cases — both new and ongoing — in a population at a given moment. While incidence tells you about the pace of disease spread, prevalence tells you about the overall burden a condition places on a community. Together, these two figures help public health leaders decide where to direct resources and how urgently to act.
Risk factors
Risk factors are the characteristics or exposures that increase the probability of developing a disease. Some risk factors are behavioral, such as smoking, physical inactivity or poor diet. Epidemiologists use statistical tools to quantify associations between risk factors and health outcomes — the analytical foundation of evidence-based prevention.
Together, these three concepts give epidemiologists a shared language for describing what is happening in a population and why. They appear in virtually every area of public health practice, from disease surveillance and outbreak response to health policy development and program evaluation.
Types of Epidemiology Studies
Epidemiologists rely on several distinct study designs, each suited to different research questions and practical constraints. Choosing the right design is one of the most consequential decisions in any investigation, as it determines what conclusions the data can and cannot support. Common study designs include:
Cohort studies: Follow a group of people over time, comparing those who were exposed to a risk factor against those who were not, to see who develops disease. They can provide strong evidence of association and, depending on design and controls, support causal inference.
Case-control studies: Work in reverse: they start with people who already have a disease (cases) and compare them to people who do not (controls), looking backward for differences in prior exposure. This design is often faster and is particularly useful for studying rare diseases.
Cross-sectional studies: Capture a snapshot of a population at a single point in time, measuring both exposure and disease status simultaneously. They are efficient for estimating disease prevalence but cannot establish whether exposure preceded disease.
Randomized controlled trials (RCTs): Are often considered the gold standard for testing interventions. Participants are randomly assigned to receive a treatment or a placebo, allowing researchers to draw the strongest causal conclusions.
No single design is universally superior. Each involves trade-offs between cost, feasibility and the strength of evidence it can produce. In practice, epidemiologists often draw on multiple study types over time to build a complete and defensible picture of a health issue.
Real-World Examples: Epidemiology in Action
Epidemiology’s real-world impact is most visible in the moments when disease spreads and public health professionals must act fast. The field’s origins trace to the 19th century when physician John Snow mapped cholera cases in London and traced the outbreak to a contaminated water pump — one of the earliest examples of epidemiological reasoning applied to save lives.
According to the American Public Health Association (APHA), more than 200 infectious diseases require active monitoring, prevention and control efforts by public health professionals. Epidemiologists are the specialists responsible for tracking these conditions in real time, identifying outbreaks early, determining how diseases are spreading and developing the evidence base for containment.
In recent years, epidemiologists were central to the COVID-19 response, tracking transmission, identifying high-risk populations and evaluating vaccine effectiveness. The same tools apply outside infectious disease: epidemiologists studying chronic conditions have linked sedentary behavior to cardiovascular disease risk, identified environmental exposures tied to childhood asthma and tracked how social determinants like income and housing shape health outcomes across communities.
Epidemiology in MPH Programs: What You’ll Learn
For MPH students, epidemiology is a core competency. Graduate programs in public health treat epidemiology as foundational because nearly every public health role, from program planning to health policy, depends on understanding how to interpret and act on population-level health data.
In Adelphi University’s CEPH-accredited online MPH program, the course Principles of Epidemiology is part of the program’s required foundational coursework. It covers foundational concepts in epidemiology and biostatistics as they apply to public health, focusing on epidemiological investigation methods, data analysis, and the use of established statistical techniques to assess population health.
Students also complete coursework in quantitative analysis, social research methods and environmental health — all disciplines that interact directly with epidemiological practice. The program’s unique focus on underserved and vulnerable populations means students learn to apply these methods where the need is greatest, developing the analytical skills to identify and address health disparities that affect communities with the least access to care.
Careers in Epidemiology: What the Job Actually Looks Like
Epidemiologists work across a wide range of settings, each with its own focus. According to BLS, the largest employers of epidemiologists are state governments (34% of the workforce) and local governments (22%), followed by hospitals, research institutions and universities. According to the National Association of County and City Health Officials (NACCHO), local health departments across the country serve as the front line of public health response, and epidemiological expertise is central to how they identify disease patterns, respond to outbreaks and protect the communities they serve.
Research epidemiologists at universities and federal agencies like the CDC investigate longer-term questions: the environmental causes of chronic illness, the effectiveness of public health interventions or the genetic factors that influence disease risk. Private-sector epidemiologists work for pharmaceutical companies, health insurers or consulting firms, applying the same analytical skills to drug safety monitoring and population risk assessment.
Salary and Job Outlook for Epidemiologists
The job outlook for epidemiologists is strong. According to BLS, employment of epidemiologists is projected to grow 16% from 2024 to 2034, much faster than the average for all occupations. Approximately 800 openings for epidemiologists are projected each year over the decade, driven in part by advances in healthcare technology that continue to surface new diseases and health threats requiring investigation.
Compensation reflects the field’s specialized training requirements. The median annual wage for epidemiologists was $83,980 in May 2024, according to BLS. According to Salary.com, the average annual salary for epidemiologists reached $93,104 as of early 2026. A master’s degree — most commonly an MPH — is the typical entry-level credential for the occupation, making graduate education a direct gateway into this growing field.
Learn more about Adelphi University’s online Master of Public Health program.
About Adelphi University’s Online MPH Program
Adelphi University’s CEPH-accredited online Master of Public Health program is a 42-credit graduate degree designed for working professionals. The curriculum covers epidemiology, biostatistics, public health policy, social and behavioral health, environmental health and healthcare finance, with a distinct focus on underserved and vulnerable populations. Students gain hands-on experience through a 180-hour practicum and a two-part capstone project. The program requires no GRE or GMAT for admission and coursework can be completed 100% online in as few as two years.
Adelphi University is a private university located in Garden City, New York, with more than 125 years of history in transforming student lives. Accredited by the Middle States Commission on Higher Education and recognized by U.S. News & World Report, Forbes, Money and The Princeton Review, Adelphi brings together small class sizes, full-time faculty and robust career services to support students from enrollment through graduation.