Active Surveillance
A system where public health officials actively seek out cases through regular contact with healthcare providers.
This glossary helps make complex public health and infectious disease terms easier to understand—for students, journalists, health professionals, policymakers, and anyone interested in these topics. As outbreaks and health threats grow more complex, so does the language used to describe them. I created this resource to provide concise, accurate definitions grounded in science and real-world experience. Whether you’re learning the basics or deepening your expertise, this glossary is here to support informed decision-making and better communication.
A system where public health officials actively seek out cases through regular contact with healthcare providers.
Tiny particles suspended in the air that can contain infectious agents and travel over longer distances than droplets.
The spread of infectious agents through aerosols that remain suspended in the air and can infect people over distances.
The spread of a disease by individuals who show no symptoms.
The proportion of people exposed to an infectious agent who become ill.
The average number of secondary cases caused by one infected person in a fully susceptible population; measles has one of the highest R₀ values.
A biofilm is primarily made up of bacteria and other microbes that attach to surfaces including living tissues and medical devices.
A strategy to vaccinate individuals who missed routine immunization doses.
The spread of disease in a population without a clear source of infection.
The process of identifying, assessing, and managing people who have been exposed to a disease to prevent further transmission.
A measurable immune response that is associated with protection against a specific disease.
The spread of disease through physical contact between an infected person and a susceptible individual.
Term has now fallen out of favor, but should be referenced for historical purposes.
Infection spread via respiratory droplets expelled during coughing, sneezing, or talking. Term has now fallen out of favor, but should be referenced for historical purposes.
A graphical representation of disease cases over time during an outbreak.
An inanimate object that can be contaminated with infectious agents and serve as a vehicle for transmission.
The spread of infectious agents via contaminated surfaces or objects.
The rate at which susceptible individuals acquire an infection over time.
Germ deniers are individuals or groups who reject, minimize, or distort the scientific consensus that microbes—such as bacteria, viruses, fungi, or parasites—are an important cause of human illness and death. The term “germ denier” captures a spectrum of beliefs that deviate from or directly oppose germ theory. At one end of this spectrum are extremists…
Germ theory is the foundational scientific principle that many diseases are caused by microorganisms—living organisms such as bacteria, viruses, fungi, or parasites that are invisible to the naked eye—that invade and multiply within a host organism. These microbes can disrupt normal body functions, trigger immune responses, and lead to a wide range of illnesses, some…
COVAX, WHO emergency use listing, national immunization programs.
The time between exposure to a pathogen and the onset of symptoms.
A set of interventions (e.g., PPE, vaccination, hand hygiene) used together to reduce disease transmission.
The minimum number of viral particles required to establish infection.
The time during which an infected individual can transmit the disease to others.
The separation of ill persons with contagious diseases from non-infected persons to prevent spread.
Monitoring disease through laboratory confirmation of pathogens.
Large-scale immunization efforts aimed at increasing population immunity quickly.
WHO goal to eliminate measles in specific regions through sustained high vaccine coverage.
Miasma theory was a widely accepted pre-modern explanation for disease, proposing that illnesses such as cholera, plague, and malaria were caused by noxious forms of bad air arising from decaying matter, filth, or swampy ground. It held that foul odors and vapors could corrupt the body and lead to disease, particularly in densely populated or…
Public health measures like isolation, quarantine, and mask-wearing used to control infectious diseases in the absence of vaccines or treatments.
The spread of infections within healthcare settings.
Case definitions, attack rates, reproductive number (R₀), superspreaders, source tracing.
A system where healthcare providers report cases of notifiable diseases to public health authorities.
Monitoring specific infectious agents through laboratory testing and genetic analysis.
Preventive medical treatment started after exposure to a pathogen to prevent infection or disease.
A formal WHO declaration for global health threats, such as major outbreaks.
Isolation separates sick individuals; quarantine restricts movement of exposed individuals to prevent spread.
A strategy of vaccinating close contacts of an infected person to limit disease spread.
The percentage of a population receiving standard vaccines through national programs.
The proportion of susceptible individuals who become infected after exposure to a contagious person.
A surveillance system that monitors disease trends using selected healthcare facilities.
Undetected disease spread due to asymptomatic or unrecognized cases.
An individual who disproportionately infects a large number of people.
Networks for collecting, analyzing, and interpreting health data to guide public health actions and evaluate interventions.
Monitoring of symptoms or clinical features rather than confirmed diagnoses to detect outbreaks early.
Terrain theory is an outdated and scientifically unsupported hypothesis that suggests disease originates primarily from internal imbalances in the body’s “terrain” (its overall internal environment), rather than from microbes, such as bacteria, viruses, fungi, and parasites. Proponents argue that a healthy internal state prevents disease, and that microbes only cause illness if the body’s terrain…
Reluctance or refusal to vaccinate despite the availability of vaccines.
The spread of pathogens by insects or other animals that transmit infectious agents from one host to another.
Children who have never received a single vaccine dose, making them highly susceptible to measles.