A mysterious death at a Russian anti-plague research facility has triggered heightened health precautions in Siberia, with nearly 200 people reportedly placed under medical observation over fears of possible pneumonic plague exposure.

The deceased has been identified in media reports as 28-year-old laboratory technician Darya Shipilova, who worked at the Irkutsk Anti-Plague Research Institute of Siberia and the Far East. She was hospitalized after developing severe pneumonia and later died.

Early reports raised concerns that Shipilova may have contracted pneumonic plague, a serious bacterial infection caused by Yersinia pestis. However, Russian health authorities have not officially confirmed plague as the cause of her death.

Russia’s public health watchdog, Rospotrebnadzor, said the worker was diagnosed with pneumonia of unknown origin and reported that testing did not detect microorganisms associated with the pathogens she handled professionally. Authorities have also said there is currently no evidence of a laboratory accident involving dangerous pathogens.

Despite those assurances, authorities have taken extensive precautions.

Nearly 200 people believed to have had contact with Shipilova have reportedly been placed under medical supervision. The hospital where she received treatment was also temporarily quarantined as officials carried out testing and infection-control measures.

So far, officials say no additional cases linked to the suspected infection have been identified. Russian authorities have described the epidemiological situation in the Irkutsk region as stable.

The case has also attracted international attention. U.S. officials said they are monitoring reports of a possible pneumonic plague case and have urged Russian authorities to provide clear and timely information.

Pneumonic plague affects the lungs and can spread between people through respiratory droplets during close contact. Although potentially deadly without rapid treatment, modern antibiotics can successfully treat the disease when administered early.

For now, the biggest question remains unanswered: what exactly caused the young laboratory worker’s death?

Until further testing provides a definitive explanation, officials continue monitoring contacts while stressing that there is currently no confirmed wider plague outbreak.