Key Terms

Here are ten key terms that people should know about epidemiology:

1. Retrospective Study: A study type that finds people with and without a disease and then goes back to find out if their health habits could have caused the disease.
2. Prospective Study: A study that starts to watch people over time in the future. The study looks at the habits of a group of people and then follows them to see who gets a disease and who doesn't.
3. Index Case: An index case is the first case of a disease to be identified, either ever or at the start of an epidemic or a seasonal (or periodic) outbreak.
4. Outbreak: A sudden increase in prevalence
5. Virus: an ultramicroscopic (20 to 300 nm in diameter), metabolically inert, infectious agent that replicates only within the cells of living hosts, mainly bacteria, plants, and animals
6. Pathogen: An agent that causes disease, especially a living microorganism such as a bacterium or fungus
7. Prevalence: The total number of cases of a disease in a given population at a specific time
8. Epidemic Disease: An epidemic disease is a disease that many people acquire over a short period
9. Endemic Disease: An endemic disease is one that is always present in a population
10. Cluster: A group of cases close in time and place.