Cross-contamination of clinical specimens with Bacillus anthracis during a laboratory proficiency test--Idaho, 2006.

On July 18, 2006, the Utah Department of Health notified epidemiologists at the Idaho Department of Health and Welfare that Bacillus anthracis, the causative agent for anthrax, had been isolated from a patient. On the same day, the Idaho epidemiologists were notified by the Idaho Bureau of Laboratories of a specimen from a second patient received for anthrax testing. The two reports resulted briefly in alerts to the Federal Bureau of Investigation (FBI) and precautionary treatment of one of the patients for anthrax. Subsequent investigation revealed that, during July 2006, the Idaho Bureau of Laboratories had been conducting a sentinel laboratory proficiency testing exercise among Idaho's hospital laboratories. The exercise included specimens with the Sterne strain of B. anthracis, a nonvirulent strain. Subsequent laboratory testing of the two patient isolates detected the Sterne strain of B. anthracis; neither patient had signs or symptoms consistent with B. anthracis infection. Further investigation revealed that the Idaho hospital laboratories that tested the two specimens had been conducting the laboratory proficiency testing exercise simultaneously, but the Idaho epidemiologists were not aware of the exercise. The two specimens had become cross-contaminated with B. anthracis in the laboratories. The findings in this report underscore the need to follow proper laboratory practices to minimize cross-contamination. In addition, to guard against false reports of anthrax, public health epidemiologists who monitor reportable diseases should be notified of upcoming proficiency testing of high-priority bioterrorism agents.