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.

  • Active Surveillance

    A system where public health officials actively seek out cases through regular contact with healthcare providers.

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  • Aerosol

    Tiny particles suspended in the air that can contain infectious agents and travel over longer distances than droplets.

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  • Airborne Transmission

    The spread of infectious agents through aerosols that remain suspended in the air and can infect people over distances.

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  • Biofilm

    A biofilm is primarily made up of bacteria and other microbes that attach to surfaces including living tissues and medical devices.

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  • Contact Tracing

    The process of identifying, assessing, and managing people who have been exposed to a disease to prevent further transmission.

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  • Droplet

    Term has now fallen out of favor, but should be referenced for historical purposes.

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  • 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.

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  • Fomite

    An inanimate object that can be contaminated with infectious agents and serve as a vehicle for transmission.

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  • 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…

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  • 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…

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  • Isolation

    The separation of ill persons with contagious diseases from non-infected persons to prevent spread.

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  • 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…

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  • Quarantine

    Isolation separates sick individuals; quarantine restricts movement of exposed individuals to prevent spread.

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  • Surveillance Systems

    Networks for collecting, analyzing, and interpreting health data to guide public health actions and evaluate interventions.

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  • 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…

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