A disease outbreak occurs when an infectious disease suddenly infects a larger number of people than usual, and the infection spreads through one or more communities. A disease outbreak may also be called an epidemic, or a pandemic when it affects a large number of countries or regions on the planet.
An important part of a disease outbreak investigation is determining the source, pathogen and mode of transmission to develop control and prevention measures. This is done using analytical epidemiology (formulating and testing hypotheses). A descriptive approach to disease outbreak investigations may also be used when the etiologic agent has already been identified.
A well-conducted outbreak investigation serves several purposes: It provides postexposure prophylaxis to those infected, halts the spread of the disease by eliminating its source and blocking transmission routes, and gives the scientific community a better understanding of etiologic agents and diseases.
In addition, outbreak investigations can give information about the spread of a well-known pathogen into new geographical areas via travelers, tourists, food and products imported from other countries, or even through domestic animals or contaminated water sources. Outbreak analysis can even lead to the discovery of new modes of transmission, such as E. coli O157:H7 that was previously associated with eating undercooked hamburgers.
Preparing for and responding to disease outbreaks requires a coordinated effort between many groups, including public health departments, veterinary services, laboratories, hospitals, CDC, and industry, as well as civil society organizations, media and individual citizens who can play an important role by helping to communicate accurate and timely information, taking precautions to protect themselves from exposure to risk-bearing materials and by practicing preventive measures such as hand washing, covering coughs and sneezes, and making sure they have access to safe and clean water and food.