Almost 200 people are under medical observation in Russia’s Siberia region after the death of a 28-year-old lab worker who may have been exposed to pneumonic plague, according to local media reports.

While Russian authorities have not confirmed her exact cause of death, the country’s consumer welfare service said Sunday that the researcher at an anti-plague institute in Irkutsk had died of “pneumonia of unknown etiology,” or origin. It said the “sanitary-epidemiological situation” in the Irkutsk region and the cities of Irkutsk and Shelekhov was “stable.”

The incident prompted health officials to place nearly 200 people who had been in contact with the researcher under precautionary medical observation, according to Russian media reports, which cited a regional leader. Maksim Modin, mayor of the Shelekhov municipal district near the border with Mongolia, said Friday that the inpatient facility where the researcher was treated had been closed for quarantine.

The pneumonic form of plague is especially contagious and “can trigger severe epidemics,” according to the World Health Organization. The WHO did not immediately respond to a request for comment Monday about the suspected case in Russia.

The State Department said it was closely monitoring the situation along with the Centers for Disease Control and other agencies.

“Many details have not been confirmed,” the department said in a statement to multiple media outlets. “We encourage Russian authorities to share accurate information quickly and openly.”

The Kremlin did not immediately respond to a request for comment.

Dr. Ashish Jha, who served as the White House Covid-19 response coordinator from 2022 to 2023, said “much more” information and transparency was needed from Moscow.

If this is an isolated case of pneumonic plague and no one else dies, “it will probably end there,” he told NBC News in an interview.

“If there were weapons programs, biological weapons programs in these labs, that would be much more concerning to me,” he said. “We need to understand that now.”

The pneumonic plague is caused by the same bacteria as the bubonic plague and can spread from person to person through airborne respiratory droplets, typically from sneezing or coughing. Medical experts say cases require rapid treatment with powerful antibiotics to prevent fatalities.

But “it’s actually very hard” for pneumonic plague to spread from person to person, Jha said.

“We may see a few more people get infected, but the chances that this becomes a larger outbreak, let alone a global pandemic, is exceedingly low,” he said.

From 2019 to 2025, 10 countries reported more than 3,800 suspected human plague cases to the WHO, the agency said last week. Six of the countries ended up having confirmed cases, most of them in the Democratic Republic of the Congo and Madagascar, with 423 deaths.