Active Surveillance
A system where public health officials actively seek out cases through regular contact with healthcare providers.
Glossary Terms
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.
-
-
Aerosol
Tiny particles suspended in the air that can contain infectious agents and travel over longer distances than droplets.
-
Airborne Transmission
The spread of infectious agents through aerosols that remain suspended in the air and can infect people over distances.
-
Asymptomatic Transmission
The spread of a disease by individuals who show no symptoms.
-
Attack Rate
The proportion of people exposed to an infectious agent who become ill.
-
Basic Reproduction Number (R₀)
The average number of secondary cases caused by one infected person in a fully susceptible population; measles has one of the highest R₀ values.
-
Biofilm
A biofilm is primarily made up of bacteria and other microbes that attach to surfaces including living tissues and medical devices.
-
Catch-Up Immunization Campaign
A strategy to vaccinate individuals who missed routine immunization doses.
-
Community Transmission
The spread of disease in a population without a clear source of infection.
-
Contact Tracing
The process of identifying, assessing, and managing people who have been exposed to a disease to prevent further transmission.
-
Correlate of Protection
A measurable immune response that is associated with protection against a specific disease.
-
Direct Contact Transmission
The spread of disease through physical contact between an infected person and a susceptible individual.
-
Droplet
Term has now fallen out of favor, but should be referenced for historical purposes.
-
Droplet Transmission
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.
-
Epidemic Curve (Epi Curve)
A graphical representation of disease cases over time during an outbreak.
-
Fomite
An inanimate object that can be contaminated with infectious agents and serve as a vehicle for transmission.
-
Fomite Transmission
The spread of infectious agents via contaminated surfaces or objects.
-
Force of Infection (FOI)
The rate at which susceptible individuals acquire an infection over time.
-
Germ Deniers
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
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…
-
Global Vaccination Policies
COVAX, WHO emergency use listing, national immunization programs.
-
Incubation Period
The time between exposure to a pathogen and the onset of symptoms.
-
Infection Control Bundle
A set of interventions (e.g., PPE, vaccination, hand hygiene) used together to reduce disease transmission.
-
Infectious Dose
The minimum number of viral particles required to establish infection.
-
Infectious Period
The time during which an infected individual can transmit the disease to others.
-
Isolation
The separation of ill persons with contagious diseases from non-infected persons to prevent spread.
-
Lab-based Surveillance
Monitoring disease through laboratory confirmation of pathogens.
-
Mass Vaccination Campaign
Large-scale immunization efforts aimed at increasing population immunity quickly.
-
Measles Elimination Target
WHO goal to eliminate measles in specific regions through sustained high vaccine coverage.
-
Miasma Theory
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…
-
Non-Pharmaceutical Interventions (NPIs)
Public health measures like isolation, quarantine, and mask-wearing used to control infectious diseases in the absence of vaccines or treatments.
-
Nosocomial Transmission
The spread of infections within healthcare settings.
-
Outbreak Investigation
Case definitions, attack rates, reproductive number (R₀), superspreaders, source tracing.
-
Passive Surveillance
A system where healthcare providers report cases of notifiable diseases to public health authorities.
-
Pathogen-based Surveillance
Monitoring specific infectious agents through laboratory testing and genetic analysis.
-
Post-Exposure Prophylaxis
Preventive medical treatment started after exposure to a pathogen to prevent infection or disease.
-
Public Health Emergency of International Concern (PHEIC)
A formal WHO declaration for global health threats, such as major outbreaks.
-
Quarantine
Isolation separates sick individuals; quarantine restricts movement of exposed individuals to prevent spread.
-
Ring Vaccination
A strategy of vaccinating close contacts of an infected person to limit disease spread.
-
Routine Immunization Coverage
The percentage of a population receiving standard vaccines through national programs.
-
Secondary Attack Rate
The proportion of susceptible individuals who become infected after exposure to a contagious person.
-
Sentinel Surveillance
A surveillance system that monitors disease trends using selected healthcare facilities.
-
Silent Transmission
Undetected disease spread due to asymptomatic or unrecognized cases.
-
Superspreader
An individual who disproportionately infects a large number of people.
-
Surveillance Systems
Networks for collecting, analyzing, and interpreting health data to guide public health actions and evaluate interventions.
-
Syndromic Surveillance
Monitoring of symptoms or clinical features rather than confirmed diagnoses to detect outbreaks early.
-
Terrain Theory
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…
-
Vaccine Hesitancy
Reluctance or refusal to vaccinate despite the availability of vaccines.
-
Vector-borne Transmission
The spread of pathogens by insects or other animals that transmit infectious agents from one host to another.
-
Zero-Dose Children
Children who have never received a single vaccine dose, making them highly susceptible to measles.