Anthrax is a communicable infectious disease transmitted from animals to humans. Humans can contact Bacillus anthracis (encapsulated, aerobic, spore-forming, rod-shaped, Gram-positive bacillus) from handling or consuming undercooked meat from infected animals. The organism can also be inhaled from animal products (e.g., wool) or during intentional release of spores (i.e., bioterrorism).

There are four forms of anthrax: cutaneous, GI, oropharyngeal, and inhalational. The incubation period for cutaneous anthrax is usually immediate or within 24 hours. There is localized skin involvement with papular lesions that turn vesicular and subsequently develop into black eschar within 7–10 days. GI anthrax usually requires an incubation period of 1–7 days. Two to 4 days after the onset of symptoms, ascites develops, which can soon be followed by shock and death. The incubation period for oropharyngeal anthrax is generally about 1–7 days marked by severe sore throat, dysphagia, and fever. Although the incubation period for inhalational anthrax (results from inspiration of 8000–50,000 spores) typically ranges from 1 to 7 days, it can be prolonged up to 2 months. Typically, the symptoms are abrupt in onset with a high fever and severe respiratory distress. Shock and death can occur within 24–36 hours.

1. Use sputum, throat cultures, blood, skin, stool, pleural fluid, CSF, or ascitic fluid specimens to isolate B. anthracis. Laboratory methods include Gram stain, culture, and PCR. Collect the appropriate blood volume (usually 8–10 mL) and number of tubes per laboratory protocol. For PCR, collect 10 mL of blood in a purple-topped tube (anticoagulant, EDTA). For both CSF and pleural fluid, collect greater than 1 mL into a sterile container. For skin lesions, two swabs are taken: one for Gram stain and culture and the other for PCR.

2. Perform procedure in a biosafety level 2 (BSL-2) microbiologic laboratory. BSL-2 practices are used in laboratories in which human-derived blood or other body fluids are being tested for infectious agents.

3. Analyze samples in a certified class II biologic safety cabinet (Figure 7.6).

4. Subculture a routine sputum, blood, or stool sample to sheep blood agar (SBA), MacConkey agar, or phenylethyl alcohol plates.

5. Incubate cultures at 35 °C–37 °C and examine within 18–24 hours of incubation.

6. Test isolates for motility, morphology, beta hemolysis, and Gram stain to differentiate colonies of B. anthracis from other bacilli.

7. Remember that B. anthracis is an encapsulated Gram-positive rod—with oval-shaped, nonswelling spores, and ground-glass appearance of colonies—and is nonmotile and nonhemolytic.

8. Soak two dry sterile swabs in vesicular fluid (previously unopened vesicle) for cutaneous anthrax.

9. Use a stool specimen for GI anthrax.

10. Use a sputum specimen for inhalation anthrax; in the later stages, collect a blood sample.

11. See Chart 7.4 for the collection of specimens for inhalation and cutaneous anthrax.

The isolation of B. anthracis rods confirms the diagnosis of anthrax.