Glossary of Terms

Common terms that you may encounter on the site.


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  • Elimination (of a disease)

    The reduction of cases of a disease so that it no longer naturally exists in a particular region. For example, measles is considered eliminated in the United States (even though a few cases per year are still imported from foreign countries) because the disease does not continuously circulate there.

  • Endemic (disease)

    A disease that constantly circulates in a particular population or geographic region. Measles, for example, is considered endemic in Great Britain because it continues to circulate freely there. In contrast, measles has been eliminated in the United States and so is no longer endemic there.

  • Epidemic

    A collection of infections by a specific disease that exceeds the number of expected infections during a particular period of time.

  • Epidemiology

    The study of diseases and how they occur at a population level. Epidemiologists study the frequency and distribution of diseases among populations.

  • Eradication (of a disease)

    The elimination of a disease from the world. To date, only one human disease—smallpox—has been eradicated. This was accomplished via a combination of surveillance and vaccination programs, whereby new cases could be detected and potentially exposed individuals vaccinated in order to halt the spread of the disease.

  • Exotoxin

    A toxin excreted into the surrounding environment by a bacterium. For example, cholera and diphtheria bacteria produce exotoxins.