Perspective^*

Biologic agents have the potential to cause as many casualties in a densely populated area as a nuclear weapon. If used in a terrorist attack on civilian populations, biologic weapons could also result in widespread social disruption and complete exhaustion of health care resources.^1,5–7

The Centers for Disease Control and Prevention (CDC) classified the major bioterrorist threats into three categories, based on the overall danger to the American public.⁸ Category A agents are the most easily weaponized and disseminated, cause the highest mortality, produce extensive social disruption, and require special public health preparedness systems. Category B agents do not cause as high mortality as category A agents, but they still result in considerable morbidity and require enhancement of current surveillance systems. Category C agents are the third-highest priority and comprise new and emerging agents that are concerning because of their potential to cause significant morbidity. The list of category A, B, and C agents is given in Table 182.1.

Bioterrorism agents are most dangerous to humans when these agents are in aerosolized form.⁶ Particles smaller than 10 mcg effectively reach the alveoli. Certain agents (e.g., anthrax, botulinum) are more resistant to environmental degradation than others (e.g., plague). Some agents (e.g., plague, smallpox) may be transmitted from person to person, thus causing high rates of dissemination and requiring strict isolation measures. Until biologic contaminants are excluded, pulmonary isolation measures should be instituted in all these patients. At present, only anthrax and smallpox have vaccines licensed by the U.S. Food and Drug Administration, and both vaccines require complex administration schedules.⁹

Surveillance and management protocols should be instituted at the hospital level for dealing with large numbers of patients who present with respiratory complaints over a short period of time. If surveillance methods do indicate a bioterrorist attack, the community must work to prevent widespread contamination, to help curb the strain on health care resources. A joint report by the CDC and the U.S. Department of Health and Human Services in February 2007 established guidelines to limit the spread of a pandemic infection.¹⁰ Measures such as the recommendation that ill individuals stay home from work or school, cancellation of large public gatherings, and the use of strict hygiene techniques in the workplace could help avert a health care crisis.

Anthrax^†

Anthrax is caused by Bacillus anthracis, a gram-positive, aerobic, spore-forming bacillus. It is considered to be the biologic agent most likely to be used in a terrorist attack. A bioterrorist attack with powder containing anthrax spores in the United States in 2001 resulted in 22 confirmed cases. The bacteria are simple to obtain and grow. The resulting spores can be aerosolized, are extremely resistant to environmental degradation, and can cause untreated mortality rates up to 50% in exposed individuals. A 1970 World Health Organization study estimated that 50 kg of anthrax spores released in a city with half a million people could cause almost 100,000 deaths.

Anthrax causes cutaneous, gastrointestinal, and pulmonary disease. Human infection, usually cutaneous, typically occurs naturally from exposure to domesticated farm animals, such as sheep and cattle. Cutaneous anthrax is responsible for more than 90% of naturally occurring infections. It initially manifests as an erythematous patch, followed by degeneration into necrotic cellulitis with black eschar similar to a brown recluse spider bite. Gastrointestinal anthrax is extremely rare and causes hemorrhagic gastroenteritis and systemic toxicity.