2001 Anthrax Attacks
Image of envelope (letter) sent to Senator Daschle in 2001

Photo Credit: U.S. Department of Justice

Anthrax attacks in September 2001, known as "Amerithrax," are an example in which workers have potential exposure to anthrax on the job. In this event, BA-laced letters, including the one pictured above, mailed to news media offices and the U.S. Congress resulted in a total of 22 people contracting anthrax through inhalation or skin exposure. These cases, including five that were fatal, included people at targeted locations, U.S. Postal Service workers at sorting facilities, and individuals handling cross-contaminated mail at the destination facilities.

Human infection with Bacillus anthracis (BA), which causes anthrax, is rare in the U.S. There have been two or fewer naturally occurring cases reported per year for the past 30 years.1 The cases that do occur in the U.S. are usually attributable to handling products from infected animals, inhaling BA spores from contaminated animal products, or eating undercooked meat from infected animals. However, humans can also be infected from contact with or inhalation of BA spores from other naturally-occurring sources (e.g., soil) or releases into the environment (e.g., accidental release from a laboratory or intentional release as a biological weapon). In 2001, letters intentionally laced with powder containing BA spores caused 22 cases of anthrax. See the Hazard Recognition page for information on job categories at highest risk for potential exposure to BA.

Since the anthrax attacks in 2001, there have been six additional cases of anthrax reported to the Centers for Disease Control and Prevention (CDC), including one case of cutaneous anthrax associated with direct exposure to livestock; one gastrointestinal case from exposure to animal hides, which were being used to make drums, that were contaminated with BA; and two additional cases each of inhalation and cutaneous anthrax.2, 3, 4, 5

In the U.S., gastrointestinal anthrax is rare. Physical examination of all food animals, combined with annual vaccination programs for livestock in states where animals have had anthrax in the past, ensures that animals remain healthy until slaughter and that the food supply is not contaminated.

Even though it can affect people, anthrax is typically considered an "enzootic" disease, meaning it occurs most commonly in animals. Animals are usually infected when they consume contaminated plants, water, or soil.6 Exposure of animals’ cuts or skin abrasions to or inhalation of BA spores in the environment (e.g., in soil) is also possible. Animal infections have been reported in nearly all states, with the highest frequency in the Midwest and West, primarily in the states of Texas, California, North Dakota, South Dakota, Minnesota, Montana, Nevada and Texas.7 These infections lead to sporadic outbreaks among domestic grazing herds (e.g., cattle, sheep, and goats) and wild animals (e.g., deer and antelope). Animal cases of anthrax are most common in developing countries and countries with no veterinary public health programs promoting routine vaccination of animals. In the U.S., the precise incidence of anthrax among animals is unknown.

1 Adams, D, Gallagher, K, Jajosky, R, Sharp, P, "Summary of Notifiable Diseases – United States, 2011" Morbidity and Mortality Weekly Report (MMWR), 60, (53):1-117 (2011).

2 "Summary of Infectious Diseases," Morbidity and Mortality Weekly Report, Centers for Disease Control and Prevention (CDC), U.S. Department of Health and Human Services (2000-2014).

3 "Inhalation Anthrax Associated with Dried Animal Hides - Pennsylvania and New York City, 2006," Morbidity and Mortality Weekly Report (MMWR), 55 (10):280-282 (2006).

4 "Cutaneous Anthrax Associated with Drum Making Using Goat Hides from West Africa -- Connecticut, 2007," Morbidity and Mortality Weekly Report (MMWR), 57 (23):628-631 (2008).

5 "Gastrointestinal Anthrax after an Animal-Hide Drumming Event -- New Hampshire and Massachusetts, 2009," Morbidity and Mortality Weekly Report (MMWR), 59 (28): 872-877 (2010).

6 Griffith J., Blaney D., Shadomy S., Lehman M., Pesik N., Tostenson S., et al., "Investigation of inhalation anthrax case, United States," Emerg Infect Dis, 20(2): 280-83 (2014).

7 Cahn, C.M. and Line, S. (Eds.), The MERCK Veterinary Manual (New Jersey: Merck & Company, 2010).