At the turn of the 20th century, the world was gripped by a plague pandemic that had spread from China to port cities around the globe. So when a 41-year-old San Franciscan named Wong Chut King died of a particularly violent disease in March 1900, there were worries that the pandemic had finally reached U.S. soil.

After examining samples from Wong’s autopsy, the head of the city’s Marine Hospital Service confirmed those fears: the plague had come to America. And unfortunately, it never left.

Wong’s death marked the beginning of the United States’ first plague epidemic, which infected at least 280 people and killed at least 172 over the next eight years (the actual numbers of cases and deaths may be higher). The disease was likely introduced by rat–infested steamships arriving at California’s shores from affected areas, mostly from Asia. But instead of alerting the public, city and state officials—including the governor of California—denied there was any plague outbreak at all.

The reason for this cover-up was partly economic. There was a fear in San Francisco and the state capital of Sacramento that if news of the plague spread, it would hurt California’s economy, says Marilyn Chase, a lecturer at the UC Berkeley Graduate School of Journalism and author of The Barbary Plague: The Black Death in Victorian San Francisco.

“There was a very real threat that California’s $40 million fresh produce industry…would be lost,” she says. With that in mind, “the state actually appealed to and secured the collaboration of the surgeon general of the United States” to keep word of the disease silent.

Official silence about the disease also entailed undermining Dr. Joseph J. Kinyoun, the head of the Marine Hospital Service in San Francisco who had identified the plague bacteria in Wong’s body. As a public health official, he was determined to stop the disease from spreading. At the same time, local politicians, business owners and newspapers were determined to discredit him, says David K. Randall, a reporter for Reuters and author of Black Death at the Golden Gate: The Race to Save America from the Bubonic Plague.

“You had the local newspapers calling [Kinyoun] a fake, calling him suspicious, implying that he was just trying to take money from the public coffers and this was all a big scam,” he says. These newspapers even suggested “he was injecting dead bodies with plague so that he looked like a hero.” Business leaders and politicians echoed this rhetoric. “A state senator in Sacramento stood on the senate floor and said that Kinyoun should be hanged for what he was doing,” he says.

This large-scale denial of the plague was also, in part, a rejection of a new type of science that few understood. Kinyoun, who is now known as the father of the National Institutes of Health, was at the forefront of the field of medical bacteriology. Unlike doctors from an earlier era, Kinyoun used a microscope to study microorganisms his patients couldn’t see. California Governor Henry Gage was particularly averse to this new science.

“[Gage] basically said: If you can’t see the disease, if you can’t see what’s happening, then how do I know it exists?” Randall says. And like many others in California, Gage wasn’t even sure white people could get the plague in the first place. “The idea was that if your ancestors had survived the plague in Europe, then you somehow evolved immunity,” he says.

Contrary to this misguided belief, the plague did infect white San Franciscans; but in the beginning, it hit residents of Chinatown the hardest. Many white residents initially remained unconcerned since they attributed the outbreak to the racist perception that Chinese immigrants were disease-ridden and dirty. Residents of Chinatown, in turn, sometimes hid the bodies of plague victims to prevent further discrimination against their community.

“People [in Chinatown] were desperate to keep it confidential, and there were very good reasons for this,” Chase says. After the first confirmed plague death, “there was a blockade against Chinatown, at which time people could not go to work, they could not get goods in or out. The people were hungry.” There was a real fear that the discovery of more plague victims would lead to more quarantines or building-burning, a crude method of fighting disease.

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Knowledge of the plague outbreak eventually managed to spread outside of California. Out-of-state newspapers picked up news of the outbreak a few weeks after Wong’s death, and Kinyoun sent federal officials regular memos about the plague’s escalation. Just as California’s political and business leaders had feared, states threatened to cut off trade with California to prevent the plague from spreading.

Still, California leaders stuck to their story. In a letter to the U.S. secretary of state cosigned by San Francisco jeans magnate Levi Strauss, Governor Gage blamed Kinyoun for the “plague fake,” as he called it, and claimed San Francisco had “never seen a living case of plague.” A year after the first plague victim died, Gage successfully convinced the federal government to relocate Kinyoun to Detroit. By then, there were about 100 known deaths from the plague.

The man who replaced Kinyoun as head of the Marine Hospital Service in San Francisco was Dr. Rupert Blue. Though he too faced resistance in fighting the plague, he had advantages over Kinyoun. He was better at communicating scientific and medical information to the public, and also better at earning the trust of the city’s Chinese community.

Blue helped end the outbreak with initiatives to clean the city and eradicate its rats, whose fleas were infecting humans with the plague. By 1908, San Francisco was essentially plague-free, and California newspapers reported this news even though they’d previously denied the plague’s existence.

However, this didn’t mean the plague had left the country. The United States still reports an average of seven human plague cases each year, according to the Centers for Disease Control and Prevention. Almost all of these cases occur in the western United States. In the summer of 2019, reports of prairie dogs with plague-carrying fleas forced parts of Colorado’s Rocky Mountain Arsenal National Wildlife Refuge to shut down.

In reporting for her book, Chase learned that scientists at the Centers for Disease Control and Prevention in Fort Collins believe the strain that now exists throughout the west originates from the strain that was first carried to U.S. shores by ship rats around 1900.

Chase says, “It was very likely the delay in controlling the San Francisco plague” allowed it to spread—and persist.