Editor's Note:This story was updated on November 18 to include reports of a third case of plague.

Three patients have been diagnosed in Beijing with the most dangerous form of the plague – the medieval disease also known as the Black Death.

The announcement sent shock waves rippling through China's northeastern capital as authorities attempted to tamp down fears of an epidemic by censoring Chinese-language news of the hospitalization.

On Tuesday, Beijing authorities announced a municipal hospital had taken in a married couple from Inner Mongolia, a sparsely populated autonomous region in northwest China, seeking treatment for pneumonic plague. One patient is stable while the other is in critical condition but not deteriorating, according to Beijing's health commission.

The Chinese Center for Disease Control and Prevention assured the public on Weibo, a Chinese social media site that is the equivalent of Twitter, that chances of a plague outbreak are "extremely low." The city's health commission has quarantined the infected patients, provided preventative care for those exposed to the couple and sterilized the relevant medical facilities, the center said.

Police are also guarding the quarantined emergency room of Chaoyang hospital, where the two infected patients were first received and diagnosed, according to Caixin, an independent Chinese news outlet.

On November 16, authorities diagnosed a third case of pneumonic plague. The man, age 55, is also from Inner Mongolia though authorities said his case was not related in any way to the couple medically evacuated to Beijing. Twenty-eight people who were in close contact with the man have been quarantined and none have exhibited symptoms of the plague.

Of the three versions of the disease, pneumonic plague is the only one that can be transmitted from one person to another by coughing, for example. The other variants are typically spread by infected fleas or animals.

Pneumonic plague has symptoms of respiratory failure similar to pneumonia. Left untreated, it is fatal.

Genetic sequencing research shows the Black Death actually originated in or near China before variations of the plague spread to Europe and Africa and killed tens of millions during the 14th century .

Chinese health authorities reassured Beijing's residents this week that the most recent cases of pneumonic plague did not pose a threat. "City residents should go to work normally and continue to seek medical treatment from hospitals. There is no need to worry about the risk of infection," the Chinese Center for Disease Control and Prevention said on its social media account.

That has not allayed widespread concern that the government is intentionally downplaying or even omitting information about the cases.

The government publicly confirmed the illness on November 12. But Li Jifeng, a doctor at Chaoyang Hospital where the plague patients received treatment, wrote in a personal blog post on Wednesday that the infected couple was first transported to Beijing nine days earlier, on November 3.

The doctor's blog post, published on China's popular messaging platform WeChat, was quickly removed by censors.

In her post, Li Jifeng claimed to be on duty at the hospital emergency room when the couple was brought in with symptoms of pneumonia. She encountered a middle-aged man who had already been feverish for ten days and his wife, who fell ill after taking care of her husband.

"After years of specialist training, I am very familiar with diagnosing and treating the majority of respiratory diseases," Li wrote online. "But this time, I kept on looking but could not figure out what pathogen caused the pneumonia. I only thought it was a rare condition and did not get much information other than the patients' history."

On Weibo, users expressed dissatisfaction with the delays in making the plague cases public.

"Don't hide things like this. Let's face whatever it is together. Cover-ups only make things worse!" one user commented in response to a Chinese news report.

For some people, official statements left much to be desired. "People must ask themselves: Are China's local hospitals qualified to diagnose and treat pneumonic plague? Do provincial level health commissions have the capacity to prevent and control the disease? Furthermore, how were the two patients infected in the first place? What's the source? These questions await further investigation and information," another Weibo user asked.

A third user quipped, "I'd thought the threats of pneumonic plague were exaggerated. But the first thing I was asked at the hospital today was, 'Have you been to Inner Mongolia recently? Do you have a fever?'"

Perhaps to allay public fears, Chinese state media has largely stayed quiet on the two newest cases of the plague. The central government has also asked digital news aggregators to "block and control" online postings related to the plague, according to The New York Times.

China has a checkered record in managing public health crises. In 2002, the central government initially refused to acknowledge a nationwide outbreak of severe acute respiratory syndrome, or SARS, an illness with flu- and pneumonia-like symptoms.

The virus traveled across borders for five months until Beijing publicly announced the epidemic. In a rare moment of honesty, Beijing officials admitted in March 2003 that the city had ten times as many infected cases as they had claimed mere months earlier. Ultimately, 329 people died.

Wary of another epidemic, China has closely monitored recent outbreaks of the plague.

Mongolia, which borders the autonomous region where the infected Chinese couple lives, reported two fatal cases of bubonic plague just this year, after the patients ate raw marmot, a species of wild rodent that often carry the offending bacterium. In Mongolia, eating marmot is thought to be good for health.

Meanwhile, these experiences with treating plague patients have led China to take a role in helping other countries contain outbreaks.

In 2017, China dispatched six public health officials to help control a local pneumonic plague outbreak in Madagascar, one of three countries hit hardest by the disease in the recent decade.

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