DESCRIPTION

Bacillus anthracis is a spore-forming, aerobic gram-positive rod that can cause acute infection (anthrax) in humans and animals and has the potential to be used as a biologic weapon due to its relative ease of dispersion, rapid systemic progression, and high mortality in those who are exposed and untreated.

EPIDEMIOLOGY

• Anthrax is primarily a zoonotic disease. Most naturally acquired anthrax infections are cutaneous. Inhalational and gastrointestinal (GI) forms are particularly rare.
  • Recently, injection anthrax has been described in Europe and is associated with injection drug use.
  • This form has not yet been reported in the United States or in the pediatric population.
• Incidence is extremely low, averaging 0 to 1 cases of cutaneous anthrax per year in the United States.
• There have been only three naturally acquired cases of inhalational anthrax in the United States since 1976.
• No human-to-human spread of inhalational anthrax has been reported.
• Rare cases of human-to-human transmission of cutaneous anthrax have been reported after direct contact with infected skin lesions.
• Anthrax has been used as an agent of bioterrorism.
• If anthrax is intentionally released, physicians must be alert for diseases caused by other potential biologic warfare agents (e.g., plague, tularemia, Q fever, smallpox, and botulism).

GENERAL PREVENTION

• Antibiotics are effective against germinating B. anthracis but not against the spores. Therefore, if prophylactic antibiotics are stopped prematurely, remaining spores can cause disease when they germinate. This phenomenon of delayed-onset disease occurs with inhalational anthrax and not with cutaneous or GI exposures.
• If the threat of transmission of B. anthracis spores is deemed credible, decontamination of skin and potential fomites (e.g., clothing) should be performed to reduce the risk for cutaneous and GI forms of the disease.
• Anthrax vaccine absorbed (AVA) is the only licensed human vaccine for preexposure prophylaxis in the United States.
  • Recommended for individuals at high risk (e.g., certain members of the military as designated by the Department of Defense, certain laboratory workers, and certain veterinary workers)
  • Primary vaccination consists of intramuscular injections at 0, 1, and 6 months, followed by booster doses at 12 and 18 months, with subsequent annual booster doses.
  • Vaccination may be considered for groups who may be at high risk in the future (e.g., emergency response workers). Following the primary vaccine series and two initial booster doses, protection can be maintained with booster doses every 3 years. If the individual becomes high risk and has not had a booster in the last 12 months, a booster should be administered.
  • The most common adverse events are related to the injection site (e.g., edema, pain, local hypersensitivity).
• Infection control
  • Immediately notify the hospital epidemiologist, infection control department, and local health department of suspected cases.
  • No data suggest that patient-to-patient transmission of inhalational anthrax occurs.
  • Standard barrier isolation precautions are recommended for all hospitalized patients with all forms of anthrax infection.
  • High-efficiency particulate air-filter masks or other measures for airborne precautions are not indicated.
  • There is no need to immunize or provide prophylaxis to patient’s contacts unless they were exposed to the aerosol.
  • If anthrax is used as a bioweapon, spores may be detected on environmental surfaces. The risk of inhalational anthrax from secondary aerosolization of these spores is uncertain.

PATHOPHYSIOLOGY

• After inhalation, wound inoculation, or ingestion, B. anthracis spores infect macrophages, germinate, and proliferate.
  • Proliferation occurs at the site of infection and in regional lymph nodes.
  • Replicating bacteria release toxins, leading to edema, hemorrhage, and necrosis.
• Incubation period depends on the route of transmission.
  • Inhalational anthrax: Infection requires inhalation of >8,000 spores; incubation period is 2 to 60 days.
  • Cutaneous anthrax: Spores enter a cut or abrasion in the skin; incubation period is 1 to 12 days.
  • GI anthrax: Spores are ingested in undercooked, infected meat; incubation period is 1 to 7 days; infection occurs in the upper (oropharyngeal lesions) or lower (intestinal lesions) GI tract.
  • Injection anthrax: Spores enter injection site with injection drug use.
• Hematogenous spread of the bacteria causes infection at other sites, including the central nervous system (CNS), liver, spleen, and kidney.