Chapter 251. Anthrax (Bacillus Anthracis)

Anthrax is an acute infectious disease caused by the gram-positive, encapsulated, nonmotile, spore-forming rod Bacillus anthracis.1,2 The incubation period is 1 to 7 days after exposure, and no person-to-person transmission is documented. Its potential as an agent of bioterrorism should prompt immediate notification of the local or state health department upon first suspicion of an anthrax-like illness. Human anthrax cases arise after exposure to infected animals or their products and rarely occur in the United States. In 2001, B anthracis spores intentionally delivered through the US Postal Serviceresulted in 22 cases of bioterrorism-related anthrax.3

Clinical Manifestations

Anthrax infections occur as cutaneous, inhaled, and gastrointestinal. All forms can progress to sepsis and meningitis. Cutaneous anthrax appears when B anthracis spores enter through a cutaneous abrasion.4 A small erythematous papule vesiculates to form a painless eschar with marked edema. Lymphadenopathy or lymphangitis may occur. Untreated, mortality is as high as 20%.

Inhalation anthrax occurs after respiratory exposure to B anthracis spores.5 Initial symptoms are nonspecific, mimicking influenza. Symptoms become fulminant over a few days, often leading to death. Mediastinal widening on chest radiograph is pathognomonic. Hemorrhagic meningitis and bacteremia are common.

Gastrointestinal anthrax follows ingestion of contaminated, undercooked meat,6 presenting with nausea, vomiting, and malaise, progressing to bloody diarrhea, gross ascites, hemorrhagic lymphadenitis, and sepsis. A pharyngeal form of anthrax occurs with profound submental swelling, adenopathy, and systemic symptoms.7 Multiple forms of anthrax have been described in children.8-15

Diagnosis

Gram stain and culture of vesicular fluid or blood confirm the diagnosis of anthrax. B anthracis grows in ordinary nutrient broth and on blood agar,2 appearing as large, gram-positive, sporulating bacilli on Gram stain. Rapid diagnostic tests are available through the Laboratory Response Network.16

Treatment and Prevention

Antibiotic resistance to penicillins and tetracyclines is assumed in bioterrorism cases until proven otherwise.1 Empiric therapy of inhalational or gastrointestinal bioterrorism-mediated anthrax includes intravenous ciprofloxacin or doxycycline plus 1 or 2 additional agents, including rifampin, vancomycin, penicillin, ampicillin, chloramphenicol, imipenem, clindamycin, and clarithromycin. Ciprofloxacin has better central nervous system penetration than doxycycline. First-line therapy for cutaneous anthrax includes either oral ciprofloxacin or doxycycline. If cutaneous lesions involve the head and neck or extensive edema is associated, combination intravenous regimens are recommended. Steroid therapy is considered for severe edema associated with cutaneous lesions and for meningitis. As spores may persist in the respiratory tract, all forms of anthrax are treated for 60 days, and therapy may be completed orally when clinically appropriate.17,18

Treatment recommendations for children include ciprofloxacin (10 mg/kg/dose intravenously transitioning to 15 mg/kg/dose orally every 12 hours, maximum 500 mg per dose) or doxycycline (2.2 mg/kg/dose intravenously transitioning to same dose orally every 12 hours, maximum 100 mg per dose), plus 1 or 2 additional agents. Amoxicillin (80 mg/kg/day divided every 8 hours, maximum 500 mg per dose) is suitable for therapy completion when B anthracis is penicillin susceptible and as prophylaxis among children and pregnant/lactating women.19 Updated recommendations regarding treatment of anthrax are available on the Centers for Disease Control and Prevention Web site at www.cdc.gov.

Standard barrier precautions are advised for patients with anthrax plus contact precautions with cutaneous lesions.16 Human anthrax vaccine is recommended for those with occupational risks6,20 and is mandated for US military personnel assigned to high-risk areas. Vaccination of exposed persons following a biological anthrax attack may be optimal protection along with 60 days of antibiotic administration.1 No data on vaccine effectiveness or safety in children are available.