A laboratory worker’s death in Siberia has triggered precautionary quarantines and international scrutiny, raising fears of pneumonic plague while leaving a central question unanswered: What actually killed her? The 28-year-old employee worked at the Irkutsk Anti-Plague Research Institute near Shelekhov. She developed pneumonia of an unknown cause and subsequently died. Russian authorities quarantined a hospital and began monitoring people who had contact with her. Preliminar