Disease outbreaks
- Slovak term: Slovenský termín
- A disease outbreak is the occurrence of cases clearly in excess of normal expectancy. The number of cases indicating the presence of an outbreak varies according to the agent, size and type of previous and existing exposure (WHO 2007a).
- Two or more confirmed cases of legionellosis occurring in the same hospital or residential institution within a six-month period (WHO 2007b).
Explanation
When an outbreak or cluster of disease occurs the cause is most often an infection, transmitted through direct person-to-person or animal-to-person contact, or via environmental or other media.
However, clusters of disease may also occur that are caused by exposure to chemicals or to radioactive materials - an example of the former is Minamata disease caused by exposure to mercury.
Investigating the cause of a disease outbreak requires careful epidemiological and toxicological investigation. In some cases it may take many years of research before the etiological agent and its mechanism of toxicity are identified. (WHO 2007a)
Example
There are many examples of disease outbreaks that are eventually shown to be caused by exposure to chemicals or toxins. Tri-ortho-cresyl phosphate, for example, is a neurotoxin that, as a contaminant of medicine, food and drink, has caused a number of outbreaks of neurological illness including so-called Jamaican ginger paralysis. In 2001 a series of unexpected deaths in dialysis patients in six countries was eventually shown to be caused by the contamination of dialysis filters with perfluoroisobutylene (WHO 2007a)
References
- WHO (2007a) Environmental health in emergencies web site
- WHO (2007b) Legionella and the prevention of legionellosis
