Around 200 people have reportedly been quarantined in Russia’s Siberian Irkutsk region following the death of a laboratory worker at a plague research institute, prompting an emergency response by health authorities amid uncertainty over the cause of her illness.

The 28-year-old worker died of pneumonia of unknown origin, and authorities have not established a link between her death and her work at the institute, Reuters reported. The World Health Organization has assessed the public health risk to the general population as low based on the information currently available.

The death prompted Anna Popova, head of Russia’s health watchdog Rospotrebnadzor, to travel to the region for an emergency meeting. Parts of the hospital in Shelekhov, where the woman died, were cordoned off, while an aluminium plant reportedly instructed workers to wear masks, Reuters reported.

Russian authorities said the institute had found no evidence of an incident involving the handling of pathogens, following social media rumours that the woman had dropped a test tube containing live bacteria.

According to a statement cited by Russia’s TASS news agency, officials identified two COVID-19 cases and two rhinovirus infections among people who had been in contact with the woman. No other infectious diseases were reported.

Irkutsk Governor Igor Kobzev said all known contacts of the deceased had been identified, examined and placed under medical supervision. He added that no new cases of institute staff seeking medical attention had been reported in recent days.

The World Health Organization said the available information suggested that the public health risk to the general population was low, while adding that it would conduct further risk assessments as more information became available.

Plague-causing bacteria, Yersinia pestis, are present among small wild mammals and their fleas in parts of Siberia. However, human plague infections are rare in Russia, Reuters reported.

Pneumonic plague, which affects the lungs, can spread through infectious respiratory droplets. The disease can be fatal if left untreated, but early diagnosis and antibiotic treatment can be effective.

US President Donald Trump offered assistance to Russia, describing the incident as a significant problem for the country. US Secretary of State Marco Rubio said Washington was closely monitoring the situation.