No Evidence of a Mild Form of Inhalational Bacillus anthracis Infection During a Bioterrorism-Related Inhalational Anthrax Outbreak in Washington, D.C., in 2001

Background. The mail-related dispersal of Bacillus anthracis spores in the Washington, D.C., area during October 2001 resulted in 5 confirmed cases of inhalational anthrax. We identified an additional 144 ill persons who were potentially exposed to aerosolized spores and whose symptoms were compatible with early inhalational anthrax but whose clinical course and nonserologic laboratory evaluation revealed no evidence for B. anthracis infection. We hypothesized that early antibiotic use could have decreased the sensitivity of diagnostic tests or that bioterrorism-related inhalational anthrax may include mild disease. Methods. Eligible patients included those with illness compatible with early inhalational anthrax who had potential exposure to B. anthracis. Patient serum samples were tested for immunoglobulin G (IgG) antibody against B. anthracis protective antigen (PA) using a sensitive enzyme-linked immunosorbant assay (sensitivity, 97.6%). Results. Of the 144 eligible patients, 66 (46%) had convalescent-phase serum samples available for testing; 29 (44%) worked in an area considered to pose a high risk of exposure to B. anthracis spores. Of the 37 patients who worked in areas that did not meet the definition of high-risk exposure, 23 (62%) worked in United States postal or other government facilities in which exposure was plausible but not documented. None of the 66 patients with convalescent-phase serum samples showed evidence of an anti-PA IgG serologic response to B. anthracis. Conclusions. These data suggest that a mild form of inhalational anthrax did not occur and that surveillance for moderate or severe illness was adequate to identify all inhalational anthrax cases resulting from the Washington, D.C., bioterrorism-related anthrax exposures.