Dhaka, Oct. 5 -- Nearly 200 people have reportedly been placed under medical observation in Russia's Siberian region of Irkutsk after the death of a worker at an anti-plague research institute prompted reports of a suspected pneumonic plague infection.

The United States is monitoring the case, while Russia's public health watchdog has not confirmed a plague infection and says the epidemiological situation in the region remains stable.

Rospotrebnadzor, Russia's public health watchdog, said the employee of the Irkutsk Anti-Plague Research Institute of Siberia and the Far East had been diagnosed with "pneumonia of unknown aetiology".

Expanded testing of samples from the patient found no microorganisms associated with her professional acti...