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Sporadic- Diseases that are seen only occasionally, and usually without geographic concentration, are called sporadic diseases. Examples of sporadic diseases include tetanus, rabies, and plague.Endemic- Diseases that are constantly present in a population within a particular geographic region are called endemic diseases. For example, malaria is endemic to some regions of Brazil, but is not endemic to the United States.
36Epidemic- Diseases for which a larger than expected number of cases occurs in a short time within a geographic region are called epidemic diseases. Influenza is a good example of a commonly epidemic disease.Pandemics- An epidemic that occurs on a worldwide scale is called a pandemic disease. For example, HIV/AIDS is a pandemic disease. The means by which a disease spreads in a population.Once scientists know that a disease is present in a population, the next question that must be answered is "how is the disease spreading?" Epidemics spread through one of two characteristic patterns.Common source spread- A disease with a common sourcewill spread through a population from a single source. All cases of the disease will have the same source of infection. Food poisoning is often associated with common source spread of infection because all the cases can usually be traced back to a portion of contaminated food. These outbreaks are usually relatively short-lived. Once the source is determined and removed, the outbreak usually stops.Propagated source spread- Propagated sourceepidemics are spread from person to person. Oneperson comes in contact with the next person and passes on the infection. These epidemics usually last longer and are more difficult to control.Common source epidemics can be subdivided into point source, continuous common source, and intermittent common source epidemics.Point Source- oIn a point sourceepidemic, the source is only causing disease for a short time. Anexample of a common point source is a potato salad that is left out for too long at a picnic. Once the food is disposed of, the source of the outbreak goes away. Continuous Common Source-oContinuous common sourcesspread the disease for an extended period of time. For example, a contaminated well in London caused a Cholera outbreak in 1854. The source of this outbreak was discovered by John Snow, who is considered to be the father of epidemiology. After the source of the outbreak was removed, the outbreak stopped.Intermittent Common Source-oIntermittent common sources cause outbreaks occasionally. Usually, there is another factor such as weather that contributes to the intermittent common sources' infectiveness. For excessive rain may cause a manure storage pit to overflow and contaminate a swimming lake with E. coli.
37SummaryOutbreaks of a disease can be classified by the extent to which they have spread and the mechanism by which it spreads.