What Is Epidemiology?

Epidemiology is a foundational discipline in public health. It is commonly defined as the study of the determinants, occurrence, and distribution of health and disease in a defined population, focusing on how diseases spread, who they affect, and why certain populations are at higher risk. This population-based perspective allows researchers and policymakers to identify risk factors, evaluate interventions, and inform evidence-based health decisions.

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Key elements of epidemiology include:

Distribution of health events
Determinants (causes and risk factors)
Defined populations
Application to disease prevention and control

What Are the Types of Epidemiology？

According to Columbia Public Health, Epidemiology addresses a broad spectrum of topics, ranging from unintentional injuries to psychosocial stress. Below are several key areas in which Columbia Mailman faculty and students conduct research and practice.

Infectious diseases
Chronic Disease (e.g., cancer, heart disease)
Environmental Epidemiology
Violence and Injury Epidemiology

What Is the Epidemiology Triangle?

The agent, the host, and the environment.

According to public health education resources from the Texas A&M University School of Public Health, the epidemiological triangle is a conceptual model used to understand how diseases occur and spread by examining the interaction among three essential components: the agent, the host, and the environment.

The U.S. Centers for Disease Control and Prevention (CDC) similarly describes the epidemiological triangle as a model developed to study health problems and better understand how infectious diseases spread within populations, making it a foundational tool in outbreak investigation and public health intervention planning.

Component	CDC Definition	Key Factors and Examples
Agent	Originally defined as an infectious microorganism or pathogen, the agent must generally be present for disease to occur, though its presence alone is not always sufficient. Over time, the definition has expanded to include chemical and physical causes of disease or injury.	• Infectious agents: viruses, bacteria, parasites, other microbes • Agent characteristics: pathogenicity, dose • Chemical agents: contaminants (e.g., L-tryptophan contaminant linked to eosinophilia-myalgia syndrome) • Physical agents: mechanical forces (e.g., repetitive motion associated with carpal tunnel syndrome)
Host	The human who can acquire the disease. Host-related factors influence exposure, susceptibility, and response to the agent and are often referred to as risk factors.	• Demographic factors: age, sex • Behavioral factors: hygiene, sexual practices, personal behaviors • Biological factors: genetic makeup, nutritional status, immune function • Medical factors: existing diseases, medications • Psychological factors
Environment	Extrinsic factors that affect the agent and the opportunity for exposure, shaping whether and how transmission occurs.	• Physical factors: climate, geography, geology • Biological factors: vectors such as insects • Socioeconomic factors: crowding, sanitation, access to health services

According to the CDC, while the epidemiologic triad is a useful framework for many infectious and injury-related conditions, it is often insufficient for explaining complex diseases such as cardiovascular disease and cancer, which typically involve multiple contributing factors rather than a single necessary cause.

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