Anthrax Letters in an Open Office Environment: Effects of Selected CDC Response Guidelines on Personal Exposure and Building Contamination

Abstract

In 2001, letters filled with a powder containing anthrax (Bacillus anthracis) spores were delivered by mail to a number of governmental and media locations within the United States. In response, the U.S. Centers for Disease Control and Prevention (CDC) provided guidelines for office personnel who might encounter a letter containing suspicious powder. These guidelines were developed during the crisis and in the absence of experimental data from laboratory or field investigations. An obvious need thus exists for quantitative and scientific verification for validation of these guidelines. This study attempts to address this need, adapting earlier work that used a multiple small office test site to create a model system in an open office test site in a vacated office building in which Bacillus atrophaeus spores (as a simulant for B. anthracis spores) were released by opening a letter. Using SF₆ as a tracer gas, smoke tubes (containing stannic chloride) to visualize airflow, culturable aerosol sampling, and aerosol spectrometry we were able to characterize airflow and unmitigated spore aerosol dissemination within the office test site. Subsequently, two scripted test scenarios were used to reproduce selected portions of the existing CDC response guidelines and a modified version where the contaminated letter opener warned co-workers to evacuate then waited 5 min before doing so himself. By not leaving together with other co-workers, the risk of the letter opener cross-contaminating others was eliminated. The total potential spore aerosol exposure of the letter opener was not affected by remaining still and waiting 5 min to allow co-workers to escape first before leaving the office. Closing office doors and quickly deactivating the heating, ventilation, and air conditioning system significantly reduced spore aerosol concentrations outside the main open office in which they had been released.

Keywords:

• Bacillus atrophaeus
• BG
• spore aerosols
• scenario-based modeling

ACKNOWLEDGMENTS

This work was carried out as Task Plan #T-750B under the U.S./ Canadian Agreement on Cooperative Research and Development Concerning Counterterrorism signed June 23, 1995 between the Secretary of Defense of the United States and the Solicitor General of Canada. The authors would like to thank Rayanne Hilsen (DRDC Suffield) for her excellent logistical and technical support. The authors would also like to thank Donnie Booher (CDC/NIOSH) for his technical support for the tracer gas experiments.

Notes

^A n = the number of replicates.

^B Significantly lower (p < 0.05 by ANOVA) than LO sampler in same scenario.

^C Significantly lower (p < 0.05 by ANOVA) than all other samplers in same scenario and from Exit sampler in the Baseline Scenario.

^A Total CFU for SKC sampler listed in this column is significantly greater than SKC samplers listed under scenario columns. P values ranged from <0.001 to 0.038. Total CFU from Samplers 4–8 were not significantly greater than any other sampler. Sampler 9 was not significantly greater than any other sampler in Scenarios 1 or 2.