Primary prevention
Primary prevention is based on limiting exposure to anthrax spores. If occupational exposure is expected, appropriate personal protective equipment and biosafety measures are recommended. Such prevention measures include designated work clothing that covers all exposed skin, eye protection, and a mask/respirator. Work clothes should be laundered on site. People should maintain good hand hygiene and avoid putting fingers into the eyes, nose, or mouth. As inhalation anthrax has been linked to the large-scale preparation of animal hides and wool, measures to maximise ventilation in these professional settings is recommended. Measures should be taken to avoid vigorously shaking or beating animal hides.
Human-to-human transmission of anthrax has primarily been reported through contact with non-intact or actively draining skin lesions, so patients with such lesions should be placed in contact precautions. Other manifestations of anthrax do not pose risk of transmission, and standard precautions are recommended.[41]
Anthrax vaccine adsorbed (AVA), a non-infectious vaccine developed from an avirulent non-encapsulated strain of Bacillus anthracis, is recommended for pre-exposure prophylaxis. It is administered as a priming series at 0, 1, and 6 months, with booster doses given at 12 and 18 months and annually thereafter. People may work in high-risk areas of exposure with appropriate personal protective equipment and biosafety measures after the priming series has been completed. A booster dose is recommended every 3 years in people who are no longer at high risk for exposure to B anthracis and who have previously completed the initial primer and booster series and want to maintain protection (e.g., emergency responders who may be at high risk in the future).[42]
Use of the anthrax vaccine should be limited to the following groups of adults aged 18-65 years who are at risk of exposure to B anthracis:
People who work with anthrax in a laboratory setting
People who handle potentially infected animals or animal products (e.g., farmers, veterinarians, livestock handlers)
Active duty military personnel deployed to areas where there is a high risk of exposure.
The vaccine is not recommended in pregnant women, people with a severe allergy to any component of the vaccine, or people with a history of severe allergy to a previous dose of the anthrax vaccine.[43] It is important for physicians to be aware of any severe allergies, including allergy to latex.
AVA is only available in the US. Other anthrax vaccines may be available in other countries, but the formulation and dose schedule may differ. For example, in the UK, a 4-dose intramuscular regimen is recommended.[44] Local guidance should be consulted.
Secondary prevention
Post-exposure prophylaxis (PEP) is recommended to prevent infection after known or suspected exposure to aerolised Bacillus anthracis spores (e.g., a bioterrorist attack). Empirical PEP regimens consist of a single antimicrobial drug with activity against B anthracis (or an anthrax antitoxin as an alternative if antimicrobial drugs are not available), plus an anthrax vaccine if indicated. The regimens recommended here are based on guidance from the Centers for Disease Control and Prevention (CDC).[1]
Antimicrobial drugs
A single antimicrobial drug is recommended. First-line antimicrobial drugs recommended for adults, pregnant/lactating women, and children ages ≥1 month to <18 years include:
Doxycycline
Ciprofloxacin
Levofloxacin
Amoxicillin/clavulanate and clindamycin are additional first-line options in children.
Regimens for PEP in neonates are available from the CDC, but are beyond the scope of this topic.
Amoxicillin or phenoxymethylpenicillin may be used if the strain of B anthracis has been determined to be penicillin susceptible.
A penicillin-class drug is the preferred option in children if the strain is found to be penicillin susceptible. However, the benefits of fluoroquinolones and tetracyclines far outweigh the risks in children for the treatment of anthrax if the strain is penicillin-resistant.
Numerous alternative antimicrobials are recommended if first-line drugs are contraindicated, not tolerated, or unavailable.
Consult your local guidelines for more information on suitable options.
Doses of antimicrobial drugs may differ to the doses used for the treatment of anthrax and you should consult your local drug information source or guidelines for more information on doses for PEP.
Duration of therapy depends on patient characteristics and the type of exposure.
In healthy nonpregnant adults ages ≥18 years, antimicrobial drugs can be discontinued 42 days after the first dose of the anthrax vaccine or 2 weeks after the last dose of the vaccine, whichever occurs later. If vaccination is not indicated, antimicrobial drugs are recommended for 60 days after an aerosol exposure. A 60-day course is also recommended in adults ages ≥66 years and those with immunocompromising conditions, regardless of vaccination status.
In pregnant/lactating women and children, antimicrobial drugs are recommended for 60 days after an aerosol exposure, regardless of vaccination status.
In all patients with nonaerosol exposures (i.e., cutaneous or ingestion), antimicrobial drugs are recommended for 7 days and vaccination is not required.
Antimicrobial drugs are preferred to anthrax antitoxins (see below) as they are more effective and easier to administer.
Anthrax antitoxin
A single anthrax antitoxin (i.e., raxibacumab or obiltoxaximab) is recommended only if antimicrobial drugs are not available.
Raxibacumab and obiltoxaximab are recommended in all patients, regardless of age and pregnancy status. Raxibacumab is preferred if coadministration of an anthrax vaccine is indicated. Anthrax immunoglobulin is not recommended for PEP.
While there is a lack of human data, raxibacumab and obiltoxaximab have been found to be effective in animal studies.[65][66] One systematic review found that adjunctive treatment with anthrax antitoxin may play a role in enhancing survival, particularly in patients for whom antimicrobial drugs alone does not work.[67]
Supplies of these drugs are held in the national stockpile for use in the event of an emergency.
Anthrax vaccines
The Advisory Committee on Immunization Practices (ACIP) recommends three subcutaneous doses of anthrax vaccine adsorbed (AVA), in conjunction with a course of antimicrobial drugs, at 0, 2, and 4 weeks post-exposure in adults ages 18-65 years. The vaccine can be administered intramuscularly during a large-scale emergency response if the subcutaneous route poses significant material, personnel, or clinical challenges that could delay or preclude vaccination. If the available anthrax vaccine supply is insufficient to vaccinate all potentially exposed persons, dose-sparing regimens may be used to expand vaccine coverage.[42] A 3- to 6-year follow-up of vaccinated UK military personnel suggests no long-term vaccine-related adverse events.[72]
A second vaccine, anthrax vaccine adsorbed (adjuvanted), is also approved in the US for PEP, in conjunction with a course of antimicrobial drugs, following suspected or confirmed exposure to B anthracis in adults ages 18-65 years. It consists of the AVA vaccine plus a novel adjuvant (CpG 7909) that binds to the Toll-like receptor 9 to enhance immune response to the protective antigen. It has the advantage of a reduced number of doses compared to the AVA vaccine (i.e., 2 doses given intramuscularly 2 weeks apart). Approval was based on phase 2 and 3 trials.[73][74] However, efficacy for PEP is based solely on studies in animal models of inhalational anthrax.
Use in older adults >65 years, pregnant/lactating women, and children ages <18 years would be guided by data available at the time of an anthrax event, and under an appropriate regulatory mechanism.
Additional new vaccines remain in early phase development, including a bivalent vaccine for anthrax and smallpox, with early animal studies demonstrating promising results.[75]
Consult your local guidelines for appropriate PEP regimens and doses.
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