Epidemiology
- Causes both human and animal disease
- Endemic worldwide
Exposure
- Military/Bacterial Warfare: may produce either cutaneous or inahlational anthrax
- Goat Hair:
- Wool: inhalational anthrax is also known as “woolsorter’s disease”
- Animal Hide Exposure:
Etiology
- Bacillus anthracis Infection
- Large spore-forming gram-positive rod
- CDC Category A Agent: potential to be easily disseminated, have higher contagiousness, have high morbidity and mortality, and require increased public health preparedness
Physiology
- Transmission and Mechanism: inhalation of 3-5 ยต Bacillus anthracis spores into alveoli
- Spore engulfment by macrophages -> carried to hilar (regional) nodes -> multiplication of organism in its vegetative state in hilar and mediastinal nodes (where anthrax toxin is produced)
- High-Grade Bacteremia may result with production of 3 toxins (protective antigen, edema factor, lethal factor)
- Protective factor binds to cell surface and facilitates endocytosis of edema and lethal factors
- Toxin released into circulation causes septic shock
- Anti-Phagocytic Capsule: enhances lethality
- Estimated LD50: 2500-55k inhaled spores (although as few as 1-3 spores may cause disease in some reported cases in 2001)
- Incubation Period: 6 days (may vary with level of exposure)
- Accidental release in Sverdlovsk: incubation period was as long as 100 days
Diagnosis
- Sputum GS/Cult+Sens:
- CXR/Chest CT patterns:
- Mediastinal Widening (due to mediastinal adenopathy and/or hemorrhagic mediastinitis):
- Patchy, Non-Segmental Infiltrates:
- Unilateral or Bilateral Pleural Effusion:
- Blood c/s: frequently positive in <12 hrs, if antibiotics have not been given
- Level A hospital labs: can isolate the organism from routine cultures and provide presumptive identification
- Level B hospital labs: can confirm
- PCR and Specific Antigen Staining Assays: available from CDC
Clinical Presentations
Cutaneous Anthrax
- Epidemiology: most common presentation
- Clinical
- Pruritic Vesicles/Papules: ultimately develop into ulcers -> eschars
- Regional Lymphadenopathy: accompanies rash
Inhalational Anthrax (Woolsorter’s Disease)
- Epidemiology: rare presentation (only 18 cases reported in US in the 20th century)
- Clinical
- Flu-Like Symptoms (fever, headache, malaise, dry cough, abdominal discomfort): occur for first few days
- Typical flu symptoms like rhinorrhea and sore throat are uncommon
- Absence of severe bronchospasm
- Biphasic Presentation (makes diagnosis difficult): patient may transiently improve without therapy, but will usually deteriorate after that with respiratory symptoms
- Hematogenous Dissemination Stage (acute): dyspnea/cyanosis/tachycardia/septic shock/fever
- Rapidly fatal within 24 hrs of hematogenous dissemination (unless treated): survival is related to time from onset of symptoms to start of antibiotics
- Pleural Effusion: present in all of the recent cases in 2001
- Hemorrhagic Mediastinitis:
- Acute Lung Injury-ARDS (see Acute Lung Injury-ARDS, [[Acute Lung Injury-ARDS]])
- CNS Infection (50% of cases): hemorrhagic meningitis/SAH
- Prognosis
- Historical Case-Fatality Rate: 80-100%
- Recent Case-Fatality Rate: 45% (presumably better due to rapid diagnosis and treatment)
GI Anthrax
- Epidemiology: very rare (has never been diagnosed in US)
Treatment
- Cipro + Clinda: notably, clinda inhibits toxin production
- Alternative: doxy + clinda
- Vanco or Rifampin: may be added to cover CNS infection
- Need to check antibiotic sensitivities, as weaponized anthrax may have altered sensitivities
- All anthrax strains are resistant to Cephalosporins and some have an inducible penicillinase
- Infection Control: standard precautions (no human-to-human transmission, regardless of type of anthrax)
- Prophylaxis: prophylaxis of close contacts is not required
- Anthrax Vaccine: available
- Acellular, contains protective antigen
- SE: mild in 63% of recipients, severe in <1% of recipients
- Pre-Exposure Regimen: 6 injections over 18 mo period with annual boosters
- Post-Exposure Prophylaxis: 3 doses of vaccine + antibiotics (cipro or doxy) x 30 days
- Alternative: cipro
- Alternative: doxy x 60-100 days
- Alternative: amox x 60-100 days (for pregnant women and children
References
- Shafazand S, Doyle R, Ruoss S. Inhalational anthrax: epidemiology, diagnosis, and management. Chest 1999; 116:1369-1376
- Franz D, Jahrling P, Friedlander A, et al. Clinical recognition and management of patients exposed to biological warfare agents. JAMA 1997; 278:399-411
- Pile J, Malone J, Eitzen E, et al. Anthrax as a potential biological warfare agent. Arch Int Med 1998; 158:429-434
- Inglesby T, Henderson T, Bartlett J, et al. Anthrax as a biologic weapon: medical and public health management. JAMA 1999; 281:1735-1745
- Dixon T, Meselson M, Guillemin J, et al. Medical progress: anthrax. N Engl J Med 1999; 341:815-826