What caused the fatal pneumonia of a Russian plague lab worker?

Fears spread from Irkutsk, Siberia, after a young researcher at an anti-plague laboratory died of pneumonia, with the World Health Organization citing initial, unconfirmed reports suggesting pneumonic plague.

Local media claimed that on September 25 she broke a test tube containing a pneumonic plague pathogen, an allegation Russia has not accepted. She entered the hospital on September 29, and on October 2 she died as the agency learned of the case.

Russia told the agency that no biosafety incident occurred at the facility and reported that health officials conducted more than 5,500 tests, finding no evidence of any dangerous pathogenic microorganisms.

Because the cause of death remains unexplained, the World Health Organization stated that Additional clinical, epidemiological and laboratory information, including confirmation of the diagnosis in the deceased laboratory worker, is required to improve confidence in the assessment.