A disease outbreak that spreads rapidly across a population over a short time frame is called an epidemic. Epidemiologists are experts in disease progression, and help direct the public health response to disease events by describing and classifying them. While the word epidemic is often associated with infectious diseases, it can also be applied to non-infectious issues like cancer or even things that don’t cause illness but still affect the health of a population such as teen vaping and obesity.
Hippocrates used the term epidemic in his book, Of the Epidemics, published in 460 BC. His meaning was that there was a rise in disease above and beyond the normal expectations for that time of year or place.
An epidemic can be caused by an already endemic disease suddenly becoming more prevalent, or when a new disease starts affecting a particular region or population. It is important to differentiate between an epidemic and a pandemic. A pandemic is a much broader and more dangerous situation than an outbreak because it spreads to multiple regions over the world, not just a single area or population.
When a disease becomes endemic, it is present to some degree all of the time in a certain population, usually because there are effective treatment options and vaccines available. For example, the flu is an endemic virus that we see in our communities all of the time. Vaccination and effective treatments have reduced the number of cases we see each year, but the virus is not yet considered completely contained or under control and continues to threaten people’s health.