This is a list of the largest known epidemics and pandemics caused by an infectious disease. Widespread non-communicable diseases such as cardiovascular disease and cancer are not included. An epidemic is the rapid spread of disease to a large number of people in a given population within a short period of time. For example, in meningococcal infections, an attack rate in excess of 15 cases per 100,000 people for two consecutive weeks is considered an epidemic.
Due to the large time spans, the first plague pandemic (6th century–8th century) and the second plague pandemic (14th century–early 19th century) are shown by individual outbreaks, such as the Plague of Justinian (first pandemic) and the Black Death (second pandemic). On the other hand, tuberculosis (TB) became epidemic in Europe in the 18th and 19th century, showing a seasonal pattern, and is still taking place globally. The morbidity and mortality of TB and HIV/AIDS have been closely linked, known as "TB/HIV syndemic". However, due to lack of sources which describe major TB epidemics with definite time spans and death tolls, they are currently not included in the following lists.