A disease outbreak occurs when cases of a contagious illness appear to be higher than expected in a community, geographical area or season. This can be the result of many factors – from poor health department surveillance and reporting, to sudden changes in population size, and even to variations in how cases are counted across jurisdictions.
A cluster of two or more cases whose investigation shows them to have a common cause, such as eating the same food. A single case of certain rare and serious diseases, such as anthrax or botulism, may elicit an outbreak-like response from investigators because of the high risk associated with these illnesses.
In 2023, vector-borne diseases remained the most frequent cause of outbreaks, accounting for over half of all reports. Haemorrhagic fevers and Ebola caused significant morbidity and mortality, as did cholera and other water-borne infections.
The key to preventing disease outbreaks lies in global health surveillance, strategic preparedness and targeted interventions. In addition, everyone can help to reduce the impact of outbreaks by washing their hands, staying hydrated, staying away from unpasteurised milk and meat, and avoiding travel to countries with high disease risks.
Our world is more interconnected than ever before, but vigilance and preparation can still reduce the risk of large-scale disease outbreaks causing severe illness, death and economic disruption. We need to continue investing in digital, laboratory, epidemiology and anthropological tools that can rapidly detect emerging and re-emerging pathogens before they turn into public health emergencies.