Origin Unknown
“I had been isolated since April 1st. Scientists state that the incubation period can be anywhere from two to fourteen days, although fourteen days, or longer, is rare. Where would I have picked it up? I had had almost no exposure to any other person for more than two weeks. In any case, by the second week, I started to feel a little better. Still unusually exhausted, but I thought that might just be quarantine malaise.” Carolyn Kormann in The New Yorker: How Did I Catch the Coronavirus? Most people who get it are wondering the same thing, and will never know the answer.
+ Buzzfeed: Convalescent Plasma Is Looking Like A Coronavirus Success Story.