Three cases of plague have been diagnosed in China, sparking widespread fears about the spread of the disease, though officials say the risk of an outbreak is low.

As Emily Feng reports for NPR, the first cases came to light last week, when authorities in Beijing announced that two infected individuals sought treatment at a hospital in the capital. The patients, a husband and wife, are from Inner Mongolia, an autonomous and sparsely populated region in the northern part of the country. They were diagnosed with pneumonic plague, one of the two main forms of infection caused by the bacteria Yersinia pestis—the other being bubonic plague, which can advance to pneumonic plague if the infection spreads to the lungs. Yersinia pestis, per the WHO, is often found in small mammals and their fleas.

Pneumonic plague is the most deadly form of the disease. It is highly contagious, spreading from person to person via infected respiratory droplets. Without medical intervention, the disease is inevitably fatal. But recovery rates are high if it is detected and treated with antibiotics within 24 hours of the onset of symptoms.

The ailing couple was quarantined, and the Chinese Center for Disease Control and Prevention said it had conducted epidemiological investigations on people who might have been exposed to the patients, according to Sui-Lee Wee of the New York Times. All “relevant sites” were also disinfected, reports Wee. The CDC assured the public on Weibo, a Twitter-like social media site, that the risks of transmission were “extremely low.”

On November 16, a third case of plague was reported in a 55-year-old man, also from Inner Mongolia. He had, according to Alex Horton of the Washington Post, killed and eaten a wild rabbit before he was taken to a hospital around 185 miles northwest of Beijing. The man was diagnosed with bubonic plague.

The Associated Press reports that 28 people who came into contact with the patient were quarantined, and displayed no symptoms of plague—like the sudden onset of fever, body aches, vomiting and nausea. As yet, there is no epidemiological evidence linking the third plague case to the earlier two, the Inner Mongolia health commission said, according to Reuters.

Over the centuries, plague has killed millions of people around the world, most famously during the Black Death, which wiped out nearly one-third of Europe’s population in the 1300s. Yersinia pestis is believed to have originated in China, spreading to the West via ships. Today, plague infections are rare, but they do happen. According to WHO, there were 3,248 cases reported worldwide between 2010 and 2015, with 584 deaths. China has experienced a small smattering of plague infections in recent years—26 cases and 11 deaths between 2009 and 2018, reports Reuters.

Though the government has attempted to reassure the Chinese public in the wake of the recent diagnoses, many have voiced concerns that officials are minimizing or even restricting information about the cases.

The first two illnesses were confirmed on November 12. But according to NPR’s Feng, Li Jifeng, a doctor at Chaoyang Hospital where the patients were treated, wrote in a blog post that the couple had been transported to the facility on November 3—nine days before an announcement was made, raising questions about the reason for the delay.

Li explained that plague cases need to be carefully investigated and verified, and announcements about them cannot be “transmitted casually.” But her post was still taken down by censors. Wee of the Times reports that censors had also instructed digital news aggregators to “block and control” discussions pertaining the news about the plague.

“Don't hide things like this,” one Weibo commenter said, per Feng. “Let’s face whatever it is together.”

Current fears about a potential plague outbreak are perhaps being fuelled by China’s handling of past health crises. In 2003, authorities there were accused of concealing the true extent of the country’s SARS outbreak—and Beijing officials ultimately admitted that the city had experienced 10 times as many cases as they had initially reported.

In the wake of that outbreak, China “vastly improved its detection and management of infectious diseases,” writes the Associated Press. And though the Chinese CDC has said that there is “no need” for Beijing residents to worry about the risk of plague infection, it has also acknowledged that remote regions of the country—like Yunnan and the Qinghai-Tibet plateau—are vulnerable to outbreaks. Officials have warned people to stay away from infected areas, and to avoid contact with rodents.