Anthrax

Epidemiology

• Anthrax can be transmitted by inhalation, ingestion, or inoculation (inhalation is the most likely during a bioterrorist attack)
• The spore form of anthrax is highly resistant to physical and chemical agents; spores can persist in the environment for years
• Anthrax is not transmitted from person to person

Clinical

• Incubation period is 1-5 days (range up to 43 days)
• Inhalation anthrax presents as acute hemorrhagic mediastinitis
• Biphasic illness, with initial phase characterized by nonspecific flu-like illness followed by acute phase characterized by acute respiratory distress and toxemia (sepsis)
• Chest x-ray findings: Mediastinal widening in a previously healthy patient in the absence of trauma is pathognomonic for anthrax
• Mortality rate for inhalation anthrax approaches 90%, even with treatment. Shock and death within 24 - 36 hours

Laboratory Diagnosis

• Laboratory specimens should be handled in a Biosafety Level 2 facility (e.g. California state Microbial Diseases Laboratory)
• Gram stain shows gram positive bacilli, occurring singly or in short chains, often with squared off ends (safety pin appearance). In advanced disease, a gram stain of unspun blood may be positive
• Distinguishing characteristics on culture include: non-hemolytic, non-motile, capsulated bacteria that are susceptible to gamma phage lysis
• ELISA and PCR tests are available at national reference laboratories

Patient Isolation

• Standard barrier isolation precautions. Patients do not require isolation rooms
• Anthrax is not transmitted person to person

Treatment

• Prompt initiation of antibiotic therapy is essential
• Antibiotic susceptibility testing is KEY to guiding treatment
• Ciprofloxicin (400 mg IV q 12 hr) is the antibiotic of choice for penicillin-resistant anthrax or for empiric therapy while awaiting susceptibility results
• All patients should be treated with anthrax vaccine if available; antibiotic treatment should be continued until 3 doses of vaccine have been administered (day 0, 14 and 28). If vaccine is unavailable, antibiotic treatment should be continued for 60 days.

Prophylaxis

• If vaccine is available, all exposed persons (as determined by local and state health depts) should be vaccinated with 3 doses of anthrax vaccine (days 0, 14 and 28)
• Start antibiotic prophylaxis immediately after exposure with ciprofloxicin (500 mg po q 12 hrs) or doxycycline (100 mg po q 12 hrs). (If strain is penicillin-susceptible, therapy can be modified to penicillin or amoxicillin.)
• Antibiotic prophylaxis should be continued until 3 doses of vaccine have been administered; if vaccine is unavailable, antibiotics should be continued for 60 days.