An epidemic is a situation where a disease is spreading quickly to a large group of people in a given area over a short period of time. It is also a term used to describe any situation that leads to a detrimental rise in health risks, such as the increase in obesity globally (often called an “obesity epidemic”).
Epidemics arise from the interaction between agents, hosts and environmental conditions. They have a dynamic nature, which means that the rate at which they spread is different every day. They eventually come to a stop when all host plants are killed or become resistant. In a similar way, an epidemic in humans can end when the virus is eliminated or when the immune system takes over.
Infectious diseases are considered to be in an epidemic phase when they are spreading easily from person to person and they have a rapid upslope on a graph (called the epidemic curve). This is what causes public health officials to implement community interventions, such as school closures and physical distancing.
The severity of a pandemic can play an important role in the cost of managing it. One study found that during lower-severity pandemics, most costs are borne by the economy as a whole (not just the health care system) due to productivity losses from people taking sick days and missing work. In contrast, high-severity pandemics tend to be largely absorbed by the health care system. During an outbreak, it is important to keep a legal document in place that designates who you want to make medical decisions for you if you are incapacitated.