A disease outbreak is the occurrence of cases of a disease that is more than expected, or that appear to be clustered by time and space. All outbreaks and suspected outbreaks of a notifiable condition must be immediately reported to the public health jurisdiction in which the patients live.
The occurrence of disease outbreaks has profound implications for the social structure and function of communities. It can destabilise the living conditions of families, and erode local economies. It can cause severe illness and death, especially among vulnerable populations. It can also threaten global supply chains and the food, water and air that sustain us all.
Disease outbreaks can be caused by infectious agents ranging from viruses to bacteria to fungi. They can be spread by person-to-person contact, animal-to-person contact, or environmental exposure (for example, the Minamata mercury poisoning). In most cases the cause of the disease outbreak is unknown and may remain undiscovered even after a thorough investigation.
The investigation of a disease outbreak requires close collaboration between public health agencies and front-line healthcare providers. The results of the investigation should be communicated clearly to stakeholders and the community, e.g., in the form of written reports, oral briefings and information through the media. A nested case-control study is the preferred study design in an outbreak investigation. The study identifies the risk factors for a group of cases and compares them with those of healthy individuals in a sampled cohort.