Bacillus anthracis aerosolization associated with a contaminated mail sorting machine

Abstract

On October 12, 2001, two envelopes containing Bacillus anthracis spores passed through a sorting machine in a postal facility in Washington, D.C. When anthrax infection was identified in postal workers 9 days later, the facility was closed. To determine if exposure to airborne B. anthracis spores continued to occur, we performed air sampling around the contaminated sorter. One CFU of B. anthracis was isolated from 990 L of air sampled before the machine was activated. Six CFUs were isolated during machine activation and processing of clean dummy mail. These data indicate that an employee working near this machine might inhale approximately 30 B. anthracis-containing particles during an 8-h work shift. What risk this may have represented to postal workers is not known, but this estimate is approximately 20-fold less than a previous estimate of sub-5 micro m B. anthracis-containing particles routinely inhaled by asymptomatic, unvaccinated workers in a goat-hair mill.

Figure 1

Sites and results of surface sampling for Bacillus anthracis with Rodac plates.

Figure 2

Bacillus anthracis air sampling: Slit Sampler Set A collected air samples for 10 minutes before and 10 min after the mail sorter was turned on. Slit Sampler Set B collected for 20 min during each period. Total air-flow rate, 33 L/min in both samplers.