after the great rains which fell the first three or four days of this month, not a single new infection of the yellow fever took place, that those then ill of it are either dead or recovered, and that there is the most respectable assurance that there is not at this time a single subject remaining under that disorder. The refugee inhabitants have been returning into the city ever since the rain, without incurring any accident. Some who had returned before the rains caught the disease.
Thomas Jefferson to Robert Gamble, November 14, 1793
In the face of coronavirus, I’m excerpting correspondence about the 1793 yellow fever epidemic in Philadelphia, the nation’s capital at the time, which killed 5,000 of the city’s 50,000 residents.
Patrick Lee’s Explanation
Even smart leaders can be wrong about cause-and-effect.
“Bad air” associated with low-lying coastal areas affected by the tides was considered to be the cause of the yellow fever late each summer. They didn’t know the real cause was disease-carrying mosquitoes which reproduced in those swamps.
Now, Jefferson reported “great rains” had cleansed Philadelphia and ended the plague, which was killing 30 residents a day in mid-September. (The real relief was cooler weather, not heavy rains.) He estimated 99% of the city’s residents who’d fled had now returned to their homes.