Five types of botulism occur in humans: foodborne, wound, infant, intestinal, and inadvertent. A sixth type, intentional or bioterror botulism, is likely to occur during our lifetimes. Each type is associated with different epidemiology and pathogenetic mechanisms. The first recognized case of botulism in the U.S. occurred in 1899 and was caused by a beef tamale.13 Food botulism was the most common form of botulism in the U.S. prior to 1980.1 Infant (or intestinal) botulism was first described in 1976 by two groups14,15 and is now the most frequently reported type of botulism in the U.S.1 Wound botulism was first described in the U.S. in 1951, with initial cases primarily due to traumatic wounds of the extremities.16 More recently, the incidence of this form of botulism has increased and has been associated with injection drug users injecting black tar heroin.17 An adult variant of infant botulism, variously called botulinal autointoxication, or hidden, adult intestinal, or adult infectious botulism was first described in 1979.18-20 Inadvertent botulism results from unintentional exposure and typically occurs in laboratory workers21 and in patients receiving therapeutic botulinum neurotoxin.22
While successful use of neurotoxin as a bioterror agent has not occurred, it is likely only a matter of time until botulism is intentionally caused by release of toxin by terrorists. The toxin's potency and lethality make it an ideal bioweapon, and has resulted in its classification by the CDC as a category A biothreat agent, the highest level. Botulinum toxin has already been released unsuccessfully by the Japanese cult Aum Shinryko.7 Both Iraq and the former Soviet Union produced botulinum neurotoxin (BoNT) for use as weapons23,24 and at least three additional countries (Iran, North Korea, and Syria) have developed or are believed to be developing BoNT as an instrument of mass destruction. Iraq produced 19,000 L of concentrated BoNT, of which 10,000 L were weaponized in missile warheads or bombs.23,25
Exposure of even a small number of civilians to botulinum neurotoxin would overwhelm the health care delivery system of any metropolitan center. Treatment of botulism requires prolonged ICU hospitalization and mechanical ventilation for up to 6 weeks. With the downsizing and closing of hospitals, most ICUs run at 80%-100% occupancy. In San Francisco, for example, there are approximately 210 ICU beds, with an average occupancy rate of greater than 90%. As few as 30 cases of botulism would fill all empty ICU beds and occupy them for up to 6 weeks. This would eliminate availability of ICU beds for postoperative patients requiring ICU care, such as organ transplantation, neurosurgery, cardiac surgery, and traumatic injuries. Patients requiring such operations would represent "collateral damage," with necessary surgery postponed, or transferred to outlying hospitals. Major civilian exposure to BoNT would have catastrophic effects. One study estimated that aerosol exposure of 100,000 individuals to toxin, as could occur with an aerosol release over a metropolitan area, would result in 50,000 cases with 30,000 fatalities.26 Such exposure would result in 4.2 million hospital days and an estimated cost of $8.6 billion. In this study, the most important factors reducing mortality and cost were early availability of antitoxin and mechanical ventilation.15 Such treatment could reduce deaths by 25,000 and costs by $8.0 billion.
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