What Is Epidemiology?

Definition

Epidemiology is the study of the distribution and determinants of health-related events, diseases, or health-related characteristics among populations, developed by John Snow in 1855.

How It Works

Epidemiology involves the use of surveillance and investigation to identify and track health problems, with the goal of preventing and controlling disease outbreaks. Epidemiologists use descriptive epidemiology to characterize and summarize the distribution of health-related events, and analytic epidemiology to examine associations and test hypotheses about the causes of diseases. The case-control study, a type of analytic epidemiology, involves comparing people with a specific disease or condition to people without the disease, to identify potential risk factors.

Epidemiologists also use cohort studies, which involve following a group of people over time to examine the development of disease, as seen in the Framingham Heart Study, which has been ongoing since 1948 and has provided valuable insights into the risk factors for cardiovascular disease. Additionally, epidemiologists use experimental studies, such as randomized controlled trials, to evaluate the effectiveness of interventions and treatments, like the Salk polio vaccine trial, which demonstrated the vaccine's efficacy in preventing polio.

The use of statistical models, such as regression analysis, allows epidemiologists to control for confounding variables and quantify the relationships between risk factors and disease outcomes. For example, a study of the relationship between air pollution and lung cancer might use regression analysis to account for the effects of smoking and occupation on the risk of lung cancer, as seen in a study by the National Cancer Institute.

Key Components

• Surveillance: the ongoing, systematic collection, analysis, and interpretation of health-related data, which allows for the early detection of disease outbreaks and the monitoring of trends over time, as seen in the Centers for Disease Control and Prevention's (CDC) surveillance of influenza.
• Investigation: the process of gathering and analyzing data to identify the causes of a disease outbreak, which involves the use of laboratory testing and interviews with affected individuals, as seen in the investigation of the Ebola outbreak in West Africa.
• Descriptive epidemiology: the characterization and summary of the distribution of health-related events, which involves the use of rates and ratios to quantify the occurrence of disease, such as the incidence rate of tuberculosis in South Africa.
• Analytic epidemiology: the examination of associations and testing of hypotheses about the causes of diseases, which involves the use of study designs such as case-control studies and cohort studies, as seen in a study of the relationship between asbestos exposure and mesothelioma.
• Experimental studies: the use of randomized controlled trials to evaluate the effectiveness of interventions and treatments, which allows for the establishment of cause-and-effect relationships, as seen in the Women's Health Initiative study of hormone replacement therapy.
• Statistical models: the use of mathematical models to analyze and interpret data, which allows for the control of confounding variables and the quantification of relationships between risk factors and disease outcomes, as seen in a study of the relationship between diabetes and cardiovascular disease.

Common Misconceptions

Myth: Epidemiology is only concerned with the study of infectious diseases — Fact: Epidemiology also examines the distribution and determinants of non-infectious diseases, such as heart disease and cancer, as seen in the World Health Organization's (WHO) study of the global burden of disease.

Myth: Epidemiology is a new field of study — Fact: Epidemiology has its roots in the work of John Snow, who used epidemiological principles to investigate a cholera outbreak in London in 1855.

Myth: Epidemiology is only used to study human diseases — Fact: Epidemiology is also used to study diseases in animals, as seen in the study of avian influenza in poultry.

Myth: Epidemiology is a purely theoretical field — Fact: Epidemiology is a highly applied field, with epidemiologists working in public health agencies, hospitals, and research institutions to investigate and control disease outbreaks, as seen in the CDC's response to the COVID-19 pandemic.

In Practice

The CDC used epidemiological principles to investigate a salmonella outbreak in the United States, which was linked to peanut butter products. The investigation involved the use of surveillance and investigation to identify the source of the outbreak, and the implementation of control measures to prevent further cases. The CDC worked with state and local health agencies to collect and analyze data, and with industry partners to recall contaminated products. The outbreak resulted in 714 reported cases of salmonella infection, and 9 deaths, with an estimated $1 billion in economic losses. The CDC's response to the outbreak demonstrates the practical application of epidemiological principles to investigate and control disease outbreaks.