Detecting and assessing outbreaks

[Extract] An infectious disease outbreak is defined as a situation whereby the rate at which new hosts become infected increases. In other words, it is an unexpected increase in disease or mortality where it does not normally occur, or is at a frequency greater than previously observed. In Figure 5.1, we provide an example of outbreak dynamics for human diseases. As demonstrated in this graph, once the infected host population reaches a critical size, the number of new cases increases exponentially. As more individuals within a population are exposed to the disease, the number of new cases eventually declines, either through host recovery and immunity or death. The disease then becomes a long-term aspect of the population dynamics, becoming endemic and either reaching equilibrium with few occasional cases, or undergoing periodic outbreaks