A researcher working at a plague research institute in Siberia died last week after being diagnosed with pneumonia of an “unknown” cause, according to multiple reports.

The woman has been identified as Darya Shipilova, an employee at the Irkutsk Anti-Plague Research Institute of Siberia and the Far East, in local news reports that say she was 28 years old, Reuters noted.

Authorities have since put in place a “comprehensive set of anti-epidemic measures,” Maxim Modin, the mayor of the Shelekhovsky district, said, including quarantining the hospital facility where the worker was treated before her death.

Rospotrebnadzor, the country’s public health watchdog, said the woman died of “pneumonia of unknown etiology,” adding that “no micro-organisms associated with the employee’s professional duties were detected in samples taken from the patient,” in an apparent attempt to defuse speculation about a possible link between the woman and her work. It also called the epidemiological situation “stable.”

Still, Anna Popova, the head of Rospotrebnadzor, traveled to Irkutsk on Friday where she sat down with Gov. Igor Kobzev and other officials for a meeting.

About 200 people are under observation for potential exposure to the mystery illness, according to local reports cited by CNN.

The World Health Organization told the network that “based on unofficial information available, the public health risk to the general population appears to be low.”

Yet, the woman’s death has prompted concern inside the country as independent local outlet Lyudi Baikala said Shipilova died of pneumonic plague — which the WHO says is “especially contagious and can trigger severe epidemics through person-to-person transmission” — citing unnamed sources, according to The Associated Press.

The U.S. State Department said it was keeping an eye on the situation with the U.S. Centers for Disease Control and Prevention and other partners.

“We encourage Russian authorities to share accurate information quickly and openly,” a spokesperson said.

U.S. Secretary of State Marco Rubio was also asked to comment on the situation Monday, telling reporters: “I don’t think it’s cause for alarm, but it is cause for focus and a cause just to keep an eye on it.”

Meanwhile, Kremlin spokesperson Dmitry Peskov urged the public to follow announcements from the Rospotrebnadzor, rather than following “rumors or speculation.”

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