The San Francisco bubonic plague outbreak was one of the biggest health crises — and controversies — of the 20th-century United States. The plague was a disease most thought had disappeared with the medieval period, but when it resurfaced, it became one of the worst epidemics in US history. The state of California was forced to contend with an illness not yet entirely understood, as government officials and the press actively covered it up. Not only did they have to pioneer treatments for the bubonic plague, but the entire problem was also wrapped up in anti-immigrant and specifically anti-Chinese racism. Some people even referred to it as the San Francisco Chinatown plague, implying a problem specific to the Chinese residents of the city.
But that wasn't the case. Blaming a select group of people meant that the cause itself — flea-infested rats carrying the same strain of plague causing deaths in China — went unaddressed. The San Francisco plague death toll rose, taking the lives of many of the city's underprivileged residents. It wasn't until a second plague swept the city, this time primarily affecting San Francisco's white population and spreading to further areas of the US, that the root cause was identified and put to rest. While modern-day humanity still deals with tragedy incurred by the flu, the plague of the early 1900s incited racist tension and social horror simply because of the ignorance of its causes and the inexplicable death it left in its wake.
Though the San Francisco plague was hardly the first major illness that residents of the continental US had to address, it was the first major outbreak of the plague. The illness — named the Black Plague or the Black Death when it ravaged Europe in the 1300s and caused some 50 million deaths — made a comeback in the 1800s, seriously affecting China and much of east Asia.
Because of global trade and increasing numbers of people emigrating and immigrating worldwide, it was only a matter of time before epidemics began to spread. However, people did not yet understand exactly how the disease was transmitted — many believed it spread through open wounds, food, or the "miasma" theory, which claimed that diseases like the plague spread through "bad air." Because of these conflicting, erroneous theories, the world wasn't prepared to respond to a wide-scale epidemic.
The first person to die in the San Francisco plague was Wong Chut King, a lumber salesman and Chinese immigrant who was found unconscious in the flophouse where he lived after suffering an intense fever. In a morbidly preemptive move, he was brought to a nearby coffin shop where he died.
Examination of his body revealed swollen lymph nodes — called buboes, hence the disease's name — consistent with a plague infection, as well as an insect bite. Flea transmission was not yet a popular theory to explain plague infection, so while it was noted, the report did nothing to quell the subsequently rampant xenophobic explanations for the disease. When microscopic investigation revealed plague bacteria in Wong Chut King's blood, Chinatown was quarantined to stop the spread, though the fleas and rats that carried the disease were not hindered by arbitrary barriers.
San Francisco's plague outbreak was concentrated in the Chinatown district, just a few blocks from what is now the Port of San Francisco. Because Chinatown was particularly overpopulated, had poor sanitation, and had many people living in poor conditions, those features were blamed for the outbreak rather than the actual cause: flea-ridden rats brought from plague-stricken China on the ships that came to the harbor. Instead of treating the cause, the city quarantined its Chinese residents.
But quarantines don't stop rats, and the disease continued to spread outside of the quarantined zones. Because conditions were poor, and racism was rampant, the quarantined residents didn't get proper medical treatment. Thus, the concentration of infected people, fleas, and rats could grow, leading to even more infections.
In the late 1800s and early 1900s, scientists and medical professionals weren't yet sure what caused the plague. The miasma theory, which suggested the disease was spread through "bad air," was popular, as were suggestions that the plague might travel through contaminated food or open wounds. The bubonic plague is actually transmitted via flea bite, with the carrier fleas often living on rats.
China was dealing with a plague outbreak of its own in the mid-late 1850s, which soon made its way to Hong Kong. Since Chinese immigrants and imports commonly made the journey to San Francisco, it was only a matter of time before the plague reached American soil.