During the Yellow Fever Epidemic of 1793 in Philadelphia, Pennsylvania, 5000 people were listed in the official register of deaths between August 1 and November 9. The vast majority of them died of yellow fever, making the epidemic in the city of 50,000 people one of the most severe in United States' history. By the end of September, 20,000 people had fled the city. The mortality rate peaked in October, before frost finally killed the mosquitoes and brought an end to the epidemic in November. Doctors tried a variety of treatments, but knew neither the origin of the fever nor that it was transmitted by mosquitoes (which was not verified until the late nineteenth century).
The mayor and a committee of two dozen organized a fever hospital at Bush Hill and other crisis measures. Men of the Free African Society volunteered to a request for their help (in the mistaken belief that people of color were immune to the disease). Black nurses aided the sick and the leaders hired additional men to take away corpses, which most people would not touch. Blacks in the city died at the same rate as whites, about 240 altogether. Some neighboring towns refused to let refugees in from Philadelphia, for fear they were carrying the fever. Major port cities such as Baltimore and New York had quarantines against refugees and goods from Philadelphia, although New York sent financial aid to the city.