An outbreak occurs when there are more cases of a disease than expected in a specific area over a specified time period. This can be due to a true increase in actual disease incidence, increased detection (detection bias), improved diagnostic procedures, or increased interest in a particular disease by the public and media (interest bias). Local health jurisdictions must report all suspected and confirmed outbreaks of diseases and their notifiable conditions, with case investigation completion or summary information required within 7 days.
An investigation of an outbreak is a complex process, and often requires multiple agencies to collaborate in the evaluation and control of the outbreak. An important step in the investigation is determining the source and transmission of the disease, which can only be done with the application of methods of descriptive and analytical epidemiology.
Outbreaks may be caused by a variety of infectious agents, including bacteria, viruses, and parasites. They can be sporadic or continuous and affect a small number of individuals or populations as large as a nation or even the world.
As with epidemics, it is unrealistic to believe that advances in communicable disease control will eliminate outbreaks. Outbreaks will continue to occur, and the need for communities, families, and individuals to take preventive measures, such as hand washing, covering cough and sneeze, and isolating ill persons, remains crucial.