According to background information in the article, on October 15, 2001, a letter containing a light tan powdery substance was opened in the mail handling area of a Senate office suite in the Hart Senate Office Building in Washington, D.C. Federal officials removed the letter and shut down the local air handling systems. The letter was subsequently confirmed to contain viable Bacillus anthracis, (anthrax) spores that were dispersible in air. The building was officially closed to the public on October 17, 2001, with access to the contaminated suite limited to forensic investigators only. This study was conducted 25 days after the initial incident, following forensic investigation and prior to initiating cleanup in the Hart Senate Office Building.

"Information regarding primary aerosolization of B anthracis, spores has been reported, but little data are available regarding secondary aerosolization indoors," the authors write. "The purpose of this investigation was to evaluate secondary aerosolization of viable B anthraci, s spores under both [minimal activity] and active office conditions."

Christopher P.Weis, Ph.D., from the U.S. Environmental Protection Agency National Enforcement Investigations Center, Denver, and colleagues collected stationary and personal air samples, surface dust and swab samples in the contaminated U.S. Senate Office suite at the Hart Building under semi-quiescent (minimal activities) and then collected additional samples after they had simulated active office conditions. The investigators evaluated size characteristics of the spores, airborne concentrations, and surface contamination and estimated secondary aerosolization of B anthracis spores.

The authors found: "Viable B anthracis, spores reaerosolized under semi-quiescent conditions, with a marked increase in reaerosolization during simulated active office conditions. Increases were observed for B anthracis, collected on ... personal air monitors during active office conditions. More than 80 percent of the B anthracis, particles collected on stationary monitors were within a ... respirable size range of 0.95 to 3.5 æm."

"This work clearly demonstrates a potential for secondary aerosolization of viable B anthracis, spores originating from contaminated surfaces in an indoor environment," the authors write. "These findings have important implications for appropriate respiratory protection, remediation and reoccupancy of contaminated office environments."