Secondary Aerosolization of Viable Bacillus anthracis Spores in a Contaminated US Senate Office

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Abstract
On October 15, 2001, a letter containing threatening language and a light tan powdery substance was opened in the mail handling area of a Senate office suite in the Hart Senate Office Building, Washington, DC. Federal officials removed the letter and shut down the local air handling systems. The letter was transported to the US Army Medical Research Institute of Infectious Disease and was subsequently confirmed to contain viable Bacillus anthracis (anthrax) spores that were dispersible in air.1 Scanning electron microscopy of the spores used in the Senate office attack showed that they ranged from individual particles to aggregates of 100 µm or more. Spores were uniform in size and appearance and the aggregates had a propensity to pulverize1 (ie, disperse into smaller particles when disturbed).