Outbreaks, endemics, epidemics and pandemics are most usually differentiated by their rate of spread.

A disease outbreak is a rise in disease cases over what is normally expected in a in a defined area, generally over a short period of time, affecting a specific population group. Foodborne diseases and avian influenza outbreaks provide frequent examples of this. These are two areas the One Health Poultry Hub is studying.

A disease is said to be endemic when it is consistently present at a low level but limited to a particular region or population. This makes the disease spread and rates predictable. For instance, malaria is considered endemic in certain countries and regions. Avian influenza has become endemic in several countries where the Hub works, e.g., Bangladesh, often with concerns about future pandemics.

An epidemic is a disease which spreads rapidly, affecting a large number of people within a community, population or region. An epidemic is usually clinically more severe than an endemic disease. Example: The Ebola epidemic in West Africa from 2014–2016.

Finally, a pandemic is an infectious disease that has spread over multiple countries or continents at the same time affecting a large number of people. While an epidemic is large, it is also generally contained or predictable in its spread. A pandemic is international and out of control.

Pandemics can lead to dramatic loss of human life worldwide, affect public health and cause significant economic, social and political disruption. The COVID-19 pandemic – which the World Health Organization (WHO) declared on 11 March 2020 – is a perfect example of this. Investigators in the Hub are contributing to better understanding the SARS CoV-2 virus and its impacts and informing the global response to it.