The U.S. State Department and the Centers for Disease Control and Prevention (CDC) announced Monday that they are closely tracking reports of a fatal suspected case of pneumonic plague linked to an anti-plague research laboratory in southern Siberia.

Health authorities in Russia’s Irkutsk region initiated emergency anti-epidemic protocols after a female worker at the Anti-Plague Research Institute in Shelekhov fell ill and died. Russian federal sanitary watchdog Rospotrebnadzor officially categorized her condition as “pneumonia of an unknown etiology,” denying that any laboratory accident or leak of pathogenic microorganisms had occurred.

However, regional officials—including Alexei Tsydenov, head of the neighboring Buryatia region—publicly stated that the worker may have succumbed to an unspecified form of the plague. Media reports indicate nearly 200 people who came into contact with the worker have been placed under medical observation, with local authorities imposing quarantine measures and mask mandates at nearby industrial facilities.

In response to the developments, a State Department spokesperson emphasized the need for international transparency.

“Many details have not been confirmed. We encourage Russian authorities to share accurate information quickly and openly,” the spokesperson said in a statement. The State Department noted that while plague is a serious bacterial disease, it occurs naturally in various parts of the world and is readily treatable with common antibiotics when identified early.

The CDC confirmed it is coordinating directly with diplomatic officials to assess any potential health risks, though Russian authorities report that all contact testing has so far returned negative.