Finding Risk-Based Switchover Points for Response Decisions for Environmental Exposure to Bacillus anthracis

ABSTRACT

In the wake of the 2001 terrorist attacks, the use of Bacillus anthracis (anthrax) in bioterrorism attacks has emerged as a realistic concern. Thus, a contingency plan is needed to inform decision-makers about which response actions are appropriate and justified under which circumstances. This study considers the decisions: (1) to undertake prophylactic antibiotic treatment; (2) to vaccinate individuals; or (3) to decontaminate the building. While these response actions are clearly justified for highly exposed individuals, a very large number of individuals exposed to very small risks in areas outside of the immediate vicinity of the release are also likely. Our results indicate that there are non-negligible risk thresholds below which response actions produce more costs than benefits. For the base case, the thresholds range from a risk of 1 in 33 for decontamination by fumigation to 1 in 6,547 for antibiotic prophylaxis and 1 in 7,108 for vaccination. A one-way sensitivity analysis on uncertain variables indicates less than an order of magnitude change in these thresholds. Benefit–cost analysis is a useful tool for assessing tradeoffs among alternative decisions, but cannot be the sole criterion in responding to incidents because of inherent limitations.

Key Words:

• Bacillus anthracis
• decision model
• risk threshold
• cost–benefit analysis
• bioterrorism
• response strategies

ACKNOWLEDGMENTS

This research was funded through the Center for Advancing Microbial Risk Assessment, supported by the U.S. Environmental Protection Agency and the U.S. Department of Homeland Security, under the Science to Achieve Results (STAR) grant program (grant number: R83236201).

Notes

*This value represents an extreme case in a much smaller facility and was considered an outlier in this analysis.