The occurrence of disease in numbers that exceeds normal expectations in a community, geographical area or season is called a disease outbreak. Outbreaks may occur among a small group of people or impact thousands across continents. Outbreaks can be caused by viruses, bacteria or parasites that spread directly between people or through the environment. Human behaviours nearly always contribute to the initiation and expansion of disease outbreaks.
The aim of outbreak investigations is to identify the pathogen and its modes of transmission and to design control and prevention measures. Several different study designs can be used in outbreak investigations, but the case-control study is considered to be the most suitable under most circumstances (Dwyer et al. 1994).
Successful outbreak investigations often deliver information about the emergence of new infectious diseases in previously unaffected areas. Besides identifying the initial infectious agent, such investigations also identify novel ways of transmission. For example, it was an outbreak investigation that revealed that the E coli O157:H7 pathogen can be transmitted through contaminated food and water. This finding enabled the development of an effective eradication strategy in the United States, i.e., by changing the manufacturing process of hamburger meat.
Outbreak investigations can be supported by modern technological systems such as regional syndromic surveillance, which allows the collection and analysis of electronic health data for the early detection of infectious disease in a defined area. This information is then shared between local, national and international authorities for the rapid identification and response to a disease outbreak.
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