In the case of plague bacteria, special dyes resulted in a characteristic purplish “bipolar staining,” meaning both ends of the sausage shape took up dye—which was why they resembled safety pins. The safety pins meant it could be plague bacilli. Which meant the next step was quarantine. Only this wouldn’t be the usual quarantine of a ship or a single house. On March 7, in a display of Sinophobia, San Francisco city officials quarantined the entire fifteen-square-block area of Chinatown, sectioning it off with ropes, and within them the roughly thirteen thousand Chinese residents living there as well—not a single one of whom was warned in advance. Beyond Wong, no further evidence of the plague had been confirmed. [...] White people were ordered out of the quarantined area because it was assumed—without evidence—that only Chinese people were responsible for and susceptible to the infection. All this for a single case of an unconfirmed disease. It was not simply an unprecedented and ignorant use of authority, but an ultimately useless one. After all, ropes aren’t particularly effective at stopping rats. And worse, scientists had known since 1897 that fleas and rats could spread the plague, but leaders in San Francisco nevertheless chose to believe that poor living conditions in Chinatown was reason enough to isolate its entire population after a single case of plague.

— Patient Zero by Lydia Kang, Nate Pedersen