A disease outbreak is an occurrence of cases of one or more diseases that is greater than expected. It may also be when two or more linked cases of the same disease are found clustered together in time and space or sharing common behaviors such as travel, eating, or work. Outbreaks can be local or affect a region, country, or even the entire world.
Historically, epidemiologists have been at the forefront of preventing disease outbreaks. For example, Edward Jenner, who observed an outbreak of smallpox in England in the 18th century and based on his observations introduced the vaccine for the disease, and John Snow who discovered contaminated water as the cause of a cholera epidemic in London in the 1850s, set the groundwork for modern outbreak investigations.
The rapid spread of new, highly virulent infectious diseases that are difficult to control underscores the need for robust public health systems and global surveillance mechanisms. In addition, new tools and techniques such as regional syndromic surveillance, bioinformatics, and rapid diagnostic methods have strengthened outbreak investigation capacity and helped to speed the response to emerging diseases.
The most commonly reported outbreak activities are epidemiology & lab analysis, healthcare and infection, prevention, and control (IPC), governance and coordination, and logistics and support. These six categories were grouped together to form the GOAL website and dataset. In general, there is a high level of overlap between these activities.