Airborne infection with Bacillus anthracis--from mills to mail

Abstract

The lack of identified exposures in 2 of the 11 cases of bioterrorism-related inhalation anthrax in 2001 raised uncertainty about the infectious dose and transmission of Bacillus anthracis. We used the Wells-Riley mathematical model of airborne infection to estimate 1) the exposure concentrations in postal facilities where cases of inhalation anthrax occurred and 2) the risk for infection in various hypothetical scenarios of exposure to B. anthracis aerosolized from contaminated mail in residential settings. These models suggest that a small number of cases of inhalation anthrax can be expected when large numbers of persons are exposed to low concentrations of B. anthracis. The risk for inhalation anthrax is determined not only by bacillary virulence factors but also by infectious aerosol production and removal rates and by host factors.

Figure

Risk for airborne infection with Bacillus anthracis in various scenarios. Home and office exposures are for 1 hour, and postal facility exposures are for 8 hours; for postal facilities, the models assume a 14.6 L/min pulmonary ventilation rate with moderate work, comparable to the rate used to estimate inhaled doses in the Manchester study. ACH, air changes per hour.