Epidemiology of bioterrorism.

Since the discovery of Iraq’s biological weapons program, concern regarding the threat of biological warfare has increased (1). Anthrax immunizations; increased nuclear, biological, and chemical defense training; improved detection systems and protective gear; and increased vigilance have been instituted to protect the military. However, the military is not the only population at risk for biological attack. To effectively counter the potentially devastating effects of an attack, we need to understand the basic epidemiologic principles of biological agents used as weapons. A biological agent is commonly portrayed as a genetically engineered organism resistant to all known vaccines and drugs, highly contagious, and able to harm thousands of people. However, alleged attacks by the Aum Shinrikyo did not result in a single illness from a biological agent (2), and the successful 1984 contamination of salad bars in The Dalles, Oregon, by a religious cult involved a common salmonella strain that was not lethal or contagious and was susceptible to antibiotics (3). Therefore, our level of suspicion and diligence in identifying and reacting to a biological attack must remain high, since the attack may not follow an expected pattern. Furthermore, a small outbreak of illness could be an early warning of a more serious attack, and recognition and prompt institution of preventive measures (such as effective vaccines and antibiotics) could save thousands of lives. To facilitate the rapid identification of a bioterrorist attack, all health-care providers and public health personnel should have basic epidemiologic skills and knowledge of what to expect in such a setting. Any small or large outbreak of disease should be evaluated as a potential bioterrorist attack. This initial investigation does not have to be time consuming or involve law enforcement. A look at the facts surrounding the outbreak to determine if anything seems unusual or indicative of bioterrorism should suffice. Since a disease outbreak can be the result of intentional contamination, the differential diagnosis of an outbreak should first be considered. The possibilities include a spontaneous outbreak of a known endemic disease, a spontaneous outbreak of a new or reemerging disease, a laboratory accident, or an intentional attack with a biological agent. Epidemiologic tools can assist in differentiating between these possibilities. The cause of a disease or even the occurrence of something unusual may be very difficult to determine, especially if the initial cases are few. Surveillance needs to be more than routine. Not only unusually high rates of …