An outbreak or an epidemic of a disease is a significant increase in the number of cases above what would be expected at a given place and time. The word comes from the Greek words epi meaning upon or above and demos meaning people (as opposed to nosos, which refers to disease at an individual level). Epidemic is often used to describe a situation where there is a general rise in health risks within society as a whole. This is sometimes referred to as an ‘obesity epidemic’.
The World Health Organization declares a disease pandemic when its spread is out of control and its case numbers are skyrocketing. A disease is endemic when it is constantly present in a population but is not yet spreading, i.e., the population is largely immune to it. It is easy for pathogens to cross from one species to another, mutate and adapt, and travel long distances – factors that contribute to the likelihood of pandemic events.
Global trends such as increasing urbanization, changes in land use and habitat, rising demand for animal protein, increasing interactions between humans and animals, increased international travel, greater connectivity between population centers, and climate change can all increase the likelihood of pandemic events, or reduce their impact through mitigation measures. In addition, a country’s risk governance capacity can also play a role in its ability to mitigate an event. Those countries with well established risk management capacities and high levels of preparedness have been shown to be able to lessen the impact of a pandemic.