Anthrax, Inhalational

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ICD Codes

A22.1 – Pulmonary anthrax

022.1 – Pulmonary anthrax


Inhalational anthrax is an often-fatal bacterial infection caused by Bacillus anthracis, an encapsulated, gram-positive, spore-forming bacillus. Extremely rare in normal circumstances, inhalational anthrax reaches a mortality rate of nearly 100% if treatment is not started in the prodromal phase.

Bacillus anthracis has been classified by the CDC as a Category A bioterrorism agent due to its high lethality, hardiness, and ease of weaponization. The spores, which are resistant to heat, UV light, microwave radiation, and many otherwise useful disinfectants, can remain dormant in soil for years. If anthrax were to be weaponized, the most likely method of dispersal would be by aerosol release. And although gastrointestinal and cutaneous forms of anthrax exist, inhalational anthrax would be the most likely result of an aerosol release. A single case of inhalational anthrax may represent a bioterrorist threat and a public health emergency.

The incubation period for inhalational anthrax is usually 1-13 days and, rarely, up to 60 days. Inhaled spores are engulfed by macrophages and taken to regional lymph nodes, where they germinate into bacteria and then spread locally and enter the bloodstream causing bacteremia and toxemia with non-specific initial symptoms resembling influenza. These initial symptoms (eg, low-grade fever, sweats, dry cough, headache, malaise, fatigue, dyspnea, and myalgias) occur for 24-48 hours, and the patient may show signs of transient improvement after 2-4 days. If antibiotic therapy has not begun up to this time, subsequent treatment, during the severe phase, is usually futile. Sudden onset of high fever and severe respiratory distress follows along with cyanosis, hypotension, shock, and sudden death. These latter fatal manifestations are believed to be the result of exotoxins secreted by the anthrax bacilli (lethal factor, edema factor, protective antigen).

Initiate treatment based on a history of exposure or contact, not laboratory test results. In addition, a strong public health response after identification of a single early case may allow for antibiotic prophylaxis with a concomitant vaccine series for other asymptomatic exposed individuals. This can be lifesaving.

Bacillus anthracis is present in both domestic and wild animals throughout the world (mainly in agricultural regions of South and Central America, Southern and Eastern Europe, Asia, Africa, the Caribbean, and the Middle East) and can be transmitted by their meat, wool, or hides. Therefore, veterinarians and those in the meat, wool, or hide processing industries are the most at risk for contracting naturally occurring inhalational anthrax. Anthrax is rarely found in animals in the United States. Person-to-person transmission of inhalational anthrax does not occur.

Prior to the terrorist events of 2001, there were 18 cases of inhalational anthrax in humans in the United States, the most recent case occurred in 1976. There were 11 cases of inhalational anthrax attributed to the terrorist events in 2001, 5 of which resulted in death. Without proper antibiotic treatment, the mortality rate for inhalational anthrax remains high; an accidental release of B. anthracis from a bioweapons factory in Sverdlovsk, Russia in 1979 resulted in an 86% mortality rate.

The anthrax vaccine is a cell-free filtrate vaccine. The CDC regulates its use. In 2002, the United States Department of Defense reintroduced the vaccination of military personnel and essential emergency civilians against anthrax.

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