Anthrax advisories and resources for King County health care providers |
Report all suspected cases of anthrax immediately to Public Health - Seattle & King County by calling 206-296-4774.
- Soil is the natural reservoir for Bacillus anthracis, the causative agent of anthrax.
- Anthrax is predominantly a disease of animals.
- Livestock or herbivores acquire infection from consuming contaminated soil or feed.
- Anthrax is endemic in parts of Asia, Latin America, Africa, and the Mediterranean.
- In the U.S., natural outbreaks among animals have occurred in the Midwest, West, Texas, and Oklahoma.
- Naturally occurring illness in humans occurs following exposure to infected animals or contaminated animal products (e.g., hair, wool, hides, and consumption of undercooked meat).
Anthrax and bioterrorism
- B. anthracis was weaponized in the former U.S. and USSR biowarfare programs.
- Anthrax spores were used to deliberately contaminate mail in 2001, resulting in 22 cases and five deaths in the Eastern U.S.
- Aerosolization is thought to be the most likely mode of dissemination of anthrax spores in a biological attack; inhalational and cutaneous anthrax are possible clinical presentations.
Microbiology and pathogenesis |
- B. anthracis is a large, nonmotile, spore-forming, aerobic or facultatively anaerobic, gram-positive bacillus.
- Hardy spores are resistant to drying, heat, and radiation.
- Spores are introduced to the body via the lungs, gastrointestinal tract or skin, phagocytosed by macrophages, and carried to regional lymph nodes.
- Spores can remain dormant in lymph nodes for up to 60 days before germinating into vegetative cells.
- Two binary toxins - edema toxin and lethal toxin - impair water homeostasis and lead to inflammation and tissue necrosis.
Cutaneous anthrax:
- Accounts for 95% of naturally occurring anthrax cases.
- The incubation period is one to seven days.
- After inoculation on skin or mucous membranes, a small, sometimes pruritic, papule or vesicle develops.
- The papule ulcerates by the second day with central necrosis and drying, is surrounded by painless, non-pitting edema, and may be encircled by fine vesicles that enlarge over the next one to two days.
- An overlying, painless black eschar forms over the ulcerated area after one to two days and sloughs off after 12 to 14 days.
- Fever and malaise are common.
- Person-to-person transmission is rare.
- With appropriate antibiotics, the case-fatality rate is less than 1%.
Inhalational Anthrax:
- The incubation period is two to 43 days (usually less than one week).
- Illness may be biphasic with an initial non-specific prodrome of symptoms such as fever, malaise, fatigue, and anorexia followed by a sudden increase in fever, respiratory distress, diaphoresis, and shock, if untreated.
- Fever, sweats, cough (minimally or non-productive), nausea/vomiting, chest discomfort, and dyspnea were common in the 2001 outbreak cases.
- Bacteremia with subsequent sepsis and meningitis may develop.
- There is no known person-to-person transmission.
- The case fatality rate was 45% in the 2001 outbreak in Eastern U.S. and 86% in the 1979 Sverdlovsk outbreak.
Gastrointestinal Anthrax:
- The incubation period is one to seven days.
- Mucosal ulcer(s) develop, followed by regional lymphadenopathy.
- Fever, abdominal tenderness, diarrhea, vomiting, and headache are common.
- Pharyngeal edema, ascites, meningitis, and gastrointestinal perforation, obstruction, or hemorrhage can occur.
- There is no person-to-person transmission.
- The case-fatality rate is 25-60%.
- Gram stain and culture of lesion, blood, cerebrospinal fluid, respiratory, and gastrointestinal specimens.
- Confirmatory testing by gamma phage and direct fluorescence assay is performed at WA State Public Health Laboratory; contact Public Health - Seattle & King County for packaging and transport instructions for clinical specimens.
- Serologic testing may be used for retrospective diagnosis.
- Chest radiograph may show a widened mediastinum, hilar adenopathy, infiltrates/consolidation, or pleural effusions.
- CT scan of the chest may show abnormalities earlier than chest x-ray; hyperdense lymphadenopathy on a non-enhanced chest CT is suggestive of anthrax.
- Nasal swabs are not useful for clinical decision-making but may be useful for epidemiologic assessment.
Standard precautions are adequate.
- Soap and water is adequate for hand washing; bleach is not necessary.
- Respiratory transmission has not been documented, and therefore isolation of patients is not necessary.
Cover cutaneous lesions and treat dressings as a biohazard waste.
Treatment and prophylaxis |
- First-line antibiotics for treatment or prophylaxis include ciprofloxacin and doxycycline.
- Patients with inhalational anthrax should be treated for 60 days with two or three antibiotics, initially IV, switching to oral therapy when clinically appropriate.
- Antibiotic prophylaxis should be provided for those with a suspected or known exposure to B. anthracis, as determined by public health officials, for 60 to 100 days post-exposure.
- Refer to www.bt.cdc.gov for current treatment and prophylaxis guidelines.
- Anthrax vaccine:
- The vaccine is prepared from cell-free infiltrates of cultures of avirulent, nonencapsulated B. anthracis.
- It is recommended as pre-exposure prophylaxis for those with occupational exposure to B. anthracis (six doses administered subcutaneously).
- The vaccine is in limited supply and not available nor indicated for pre-exposure use in the general public.
- Adverse reactions include local erythema, pain, fever, chills, myalgia, and nausea.
- New vaccines are in development and alternative dosing schedules and route of administration are under investigation.
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