datory for these workers until the 1960s and so cannot account for the low rate of inhalational disease (Inglesby et al., 1999).

Other forms of anthrax are also rare in the United States. Until the bioterrorist events in the autumn of 2001, a total of 238 anthrax cases had been reported since 1955; of those, 95 percent were cutaneous infections (Brachman and Friedlander, 1999; CDC, 2001a). In 2000, one reported case of cutaneous anthrax occurred (CDC, 2001a) and possible cases of gastrointestinal infection were associated with the consumption of contaminated meat (CDC, 2000b).

In the autumn of 2001 the United States experienced an outbreak of anthrax due to bioterrorism. Exposure to letters containing B. anthracis spores sent through the U.S. mail resulted in seven confirmed and five suspected cutaneous cases and 11 confirmed inhalational cases (CDC, 2001e). The victims included postal workers (Gallagher and Strober, 2001), employees of print and broadcast media organizations, and at least one infant (Roche et al., 2001).

Anthrax has also been part of biological warfare programs in some countries. In 1979 in Sverdlovsk, Russia, an apparently accidental release of aerosolized spores from a military facility resulted in 68 deaths among 79 individuals with reported cases of inhalational anthrax (Meselson et al., 1994).

Clinical Features

The outbreak of inhalational and cutaneous anthrax in the United States during the autumn of 2001 produced far more clinical and public health experience with the disease than had occurred in many decades. Both the outbreak and the outcomes of individual cases showed considerable differences from previous classic descriptions. The anthrax spores appeared to have been processed intentionally to enhance their most dangerous properties. They were finely milled and rendered nonpolar to maintain the very small particle size necessary for inhalation and to promote prolonged aerosolization. Naturally occurring spores tend to adhere quickly to each other and to surfaces.

Improvements in both the speed of diagnosis and clinical management resulted in the survival of at least some of those who contracted inhalational anthrax, which would not have been expected on the basis of earlier experience (Brown, 2001). Analysis of this new information on the clinical course of disease was continuing as the committee completed this report. In particular, both the inoculum associated with infection in different individuals and the duration of antibiotic treatment necessary for survival after infection remain uncertain. Although every effort was made to include

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