The occurrence of disease in excess of what would be expected within a community, region or country. Disease can be borne naturally, transmitted by animals, or spread by humans in ways that may involve contact with an infectious agent. Whether an outbreak is occurring locally, regionally or nationally or internationally, it can quickly grow into a pandemic, affecting the health of individuals and communities across large geographic areas.
When cases of a disease exceed the expected number, an outbreak is declared. The number of cases can be determined from public health department surveillance and disease registries, or from hospital discharge records. However, the number of cases can vary from day to day and even from year to year due to variations in reporting procedures or sudden changes in population size.
An outbreak of a foodborne illness is declared when the number of cases in a given time period exceeds what is normally expected in the same time frame. Outbreaks can be confined to a single food item or an entire product line or distribution channel.
Infectious disease outbreaks can have significant economic impacts and are especially difficult in low- and middle-income countries with weak institutions, legacy legacies of political instability and inadequate investment in health sectors. These impacts include both short-term fiscal shocks and longer-term negative impacts on economic growth. In addition, public health measures such as quarantines and school and workplace closures have the potential to cause social disruption. Historically, these measures have resulted in discrimination against minority populations linked to outbreak foci, such as during the Black Death and in the 2014 Ebola epidemic in West Africa.