24/7 Tempo has compiled a list of the 20 worst epidemics and pandemics in history. An epidemic is defined as the widespread occurrence of an infectious disease in a community at a particular time.

Outbreaks of disease have impacted the lives of individuals and communities throughout history. Whether it's an epidemic (a somewhat localized influx of cases) or a pandemic (a global phenomenon ...

Some of the biggest pandemics in history include the bubonic plague, cholera and smallpox ... The 1918-1920 outbreak was the worst pandemic in history, killing 50 to 100 million people.

The plague is responsible for the two largest and most deadly pandemics in human history. However, the ebb and flow of these, why some die out and others persist for years has confounded scientists.