have emerged on the part of some people about the adverse health out-comes that might be associated with use of the vaccine.

THE DISEASE

Anthrax is caused by infection with Bacillus anthracis, a gram-positive, nonmotile, spore-forming organism (Brachman and Friedlander, 1999; Dixon et al., 1999). Exposure to the spores of this one organism can cause three different forms of disease—cutaneous, gastrointestinal, or inhalational anthrax—depending on the site of infection. Cutaneous anthrax is the most common and the most treatable form; inhalational anthrax is rare but poses a much greater risk of death.

Epidemiology

Anthrax is found worldwide and is transmitted primarily through spores that are highly resistant to heat, drought, and many disinfectants (Dixon et al., 1999). It is primarily a disease of wild and domestic animals, especially herbivores such as cattle, sheep, and goats. Animals can be infected through exposure to spores in contaminated grazing areas, contaminated feed, or infected carcasses (Friedlander, 2000). Humans in agricultural settings can be infected through contact with infected animals or contaminated animal products. Human infections also occur in industrial settings where contaminated animal products such as wool, hair, hides, or meat are processed. Most human cases in either agricultural or industrial settings are cutaneous. Inhalational anthrax is generally seen only in industrial settings because conditions where a sufficiently large number of spores are aerosolized in an enclosed area do not generally occur naturally (Brachman and Friedlander, 1999). Person-to-person transmission is not known to occur with inhalational anthrax and has rarely been reported with other forms of the disease (Friedlander, 2000).

The worldwide incidence of anthrax in humans is difficult to determine, but the annual number of cases in the 1980s and 1990s is estimated to have been about 2,000, down from an estimated 20,000 to 100,000 cases in 1958 (Brachman and Friedlander, 1999). During the 19th century, “wool-sorters’ disease,” or inhalational anthrax, was fairly common among workers handling animal hides, hairs, or wools. Approximately 200 cases were reported in the United States before 1900 (Plotkin et al., 1960). Only 18 cases of inhalational anthrax were reported in the United States in the 20th century, despite evidence of extensive exposure of workers in goat hair-processing mills to aerosolized spores (Inglesby et al., 1999). In 1957, five cases of inhalational anthrax, four of them fatal, occurred at a goat hair-processing mill in New Hampshire. Vaccination did not become man-



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