Surface sampling methods for Bacillus anthracis spore contamination

During an investigation conducted December 17-20, 2001, we collected environmental samples from a U.S. postal facility in Washington, D.C., known to be extensively contaminated with Bacillus anthracis spores. Because methods for collecting and analyzing B. anthracis spores have not yet been validated, our objective was to compare the relative effectiveness of sampling methods used for collecting spores from contaminated surfaces. Comparison of wipe, wet and dry swab, and HEPA vacuum sock samples on nonporous surfaces indicated good agreement between results with HEPA vacuum and wipe samples. However, results from HEPA vacuum sock and wipe samples agreed poorly with the swab samples. Dry swabs failed to detect spores >75% of the time when they were detected by wipe and HEPA vacuum samples. Wipe samples collected after HEPA vacuum samples and HEPA vacuum samples collected after wipe samples indicated that neither method completely removed spores from the sampled surfaces.