A disease outbreak is an unusual aggregation of cases of the same illness that exceeds what is expected in a community, geographic area, or season. Outbreaks may be caused by infectious agents transmitted by person to person or from animal reservoirs, including mosquitoes and ticks. They also may occur when human behaviours facilitate their spread, such as poor personal hygiene, crowded living conditions, inadequate vaccination programs and travel.
An important first step in identifying an outbreak is to compare current case counts with expected numbers. This can be done through health department surveillance records, disease registries and hospital discharge data.
In addition, health authorities should monitor for evidence that the number of cases may be increasing due to changes in reporting practices and other factors such as sudden fluctuations in population size. It is also important to establish the cause of the outbreak. This involves determining the pathogen or organism responsible, and how it was transmitted, including by what route(s).
The next steps are to respond, control and evaluate the outbreak. In the response stage, the aim is to ensure public safety and minimize damage to property and the economy. This includes controlling the disease through treatment, contact tracing and environmental control measures. The control stage involves changing public health policies to prevent the recurrence of an outbreak. Finally, the evaluation stage involves assessing how well the response and control measures have worked to manage the outbreak.