The US Capitol Bioterrorism Anthrax Exposures: Clinical Epidemiological and Immunological Characteristics
1Infectious Diseases Directorate, 2Combat Casualty Directorate, and 3Biological Defense Research Directorate, Naval Medical Research Center, Silver Spring, 4Infectious Diseases Service, National Naval Medical Center, and 5Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, 6Department of Molecular Microbiology and Immunology, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, and 7Henry M. Jackson Foundation, Rockville, Maryland; 8Office of the Attending Physician to Congress, United States Capitol, Washington, DC
Background.
Bioterrorism‐related anthrax exposures occurred at the US Capitol in 2001. Exposed individuals received antibiotics and anthrax vaccine adsorbed immunization.
Methods.A prospective longitudinal study of 124 subjects—stratified on the basis of spore exposure, nasopharyngeal culture results, and immunization status from inside and outside an epidemiologically defined exposure zone—was performed to describe clinical outcome and immune responses after Bacillus anthracis exposure. Antibody and cell‐mediated immune (CMI) responses to protective antigen (PA) and lethal factor were assayed by enzyme‐linked immunosorbent assay and fluorescence‐activated cell sorting.
Results.Antibody and CMI dose‐exposure responses, albeit generally of low magnitude, were seen for unimmunized subjects from inside, within the perimeter, and outside the exposure zone and in nonexposed control subjects. Anti‐PA antibody and CMI responses were detected in 94% and 86% of immunized subjects. No associations were seen between symptoms and exposure levels or immune responses.
Conclusions.Anthrax spores primed cellular and possibly antibody immune responses in a dose‐dependent manner and may have enhanced vaccine boost and recall responses. Immune responses were detected inside the perimeter and outside the exposure zone, which implies more‐extensive spore exposure than was predicted. Despite postexposure prophylaxis with antibiotics, inhalation of B. anthracis spores resulted in stimulation of the immune system and possibly subclinical infection, and the greater the exposure, the more complete the immune response. The significance of low‐level exposure should not be underestimated.
Received 13 March 2006; accepted 27 June 2006; electronically published 6 December 2006.
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(See the editorial commentary by Hadler, on pages 163–4.)
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Presented in part: 40th Annual Meeting of the Infectious Disease Society of America, Chicago, 27 October 2002 (late breaker abstract, oral presentation); American Society of Tropical Medicine and Hygiene, Denver, 11 November 2002 (late breaker abstract, oral presentation).
Potential conflicts of interest: none reported.
Financial support: US Army Medical Research Material Command (funds allocated to the Naval Medical Research and Development Center, work units N3239802RCCDD001 B998 and 61102A.S13.F.A0009). The funding source had no impact on design, conduct, and reporting of the study.
The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Navy, the Department of Defense. nor the US Government.
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D.L.D. and D.A.F. contributed equally to the study.
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Present affiliations: Naval Medical Research Center Unit 2, Jakarta, Indonesia (G.T.B.); Naval Medical Research Center Detachment, Lima, Peru (D.L.B. and G.J.M.).