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Biosecurity News in Brief
Study Finds Capitol Hill Anthrax Exposure More Widespread than Previously ThoughtBy Shana Deitch and Jennifer Nuzzo, January 12, 2007 A new study to be published in the January 15, 2007, edition of the Journal of Infectious Diseases (JID) provides an epidemiological and immunological analysis of individuals exposed to Bacillus anthracis spores during the 2001 anthrax attack on Capitol Hill.[1] The investigators examined how exposure dose, anthrax vaccination, and post-exposure prophylaxis influenced immune responses and clinical outcomes. According to the authors, this study represents “the first comprehensive longitudinal study of the epidemiological and immunological characteristics of B. anthracis exposure in humans, in a bioterrorism-related outbreak, and with postexposure prophylaxis with antibiotics and AVA.”[1] Following the anthrax letter attacks on Capitol Hill in October 2001, individuals were offered antibiotic prophylaxis and/or anthrax vaccine adsorbed (AVA), depending on their level of exposure and as determined both by nasopharyngeal culture results and by their proximity to Senator Daschle’s office (where the envelope was opened) and to letter within the Capitol complex. The study specifically investigated the extent to which anthrax exposure primed the immune response in vaccinated and unvaccinated individuals, and if so, whether immune priming improved individuals’ response to anthrax vaccine.[1] The authors found that initial exposure to anthrax activated the immune responses in both vaccinated and unvaccinated individuals in a dose-dependent manner. This suggests that despite “postexposure prophylaxis with antibiotics, inhalation of B. anthracis spores resulted in stimulation of the immune system.”[1] Immune responses observed among individuals who never developed symptoms suggest that exposure to anthrax spores may produce subclinical infection. Furthermore, exposure to anthrax spores also enhanced the vaccine-associated immune response in subjects who were immunized immediately after exposure and in those previously immunized.[1] Researchers also detected immune responses in persons outside the exposure zone, indicating that exposure to anthrax may have been more widespread than originally thought. The investigators point out that nasopharyngeal culture results were a poor predictor of exposure and suggest that the “threat of exposure may extend beyond epidemiologically defined” exposure zones.[1] Given the immune response of individuals outside of the exposure zone, the authors caution that “the significance of low-level exposure should not be underestimated.”[1] Experts suggest that this study highlights the significance of immunological indicators of possible anthrax infection. In an accompanying editorial commentary to the JID article, James Hadler notes that this study suggests that had more sensitive clinical assays been conducted, determination of anthrax exposure among postal workers in Connecticut and New York—where spore-containing envelopes were also sent—may have been made differently.[2]
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