Differential Diagnosis: The prodromal phase of respiratory anthrax resembles influenza; however coryza, nasal congestion, and sneezing are typically absent with anthrax and influenza has a more rapid progression (usually far less than a day). Many other systemic infectious diseases may mimic the prodrome of respiratory anthrax. Other potential bioterrorism agents that may be associated with flu-like prodromes (Yersinia pestis, Coxiella burnetii, Francisella tularensis, and smallpox) need to be considered for an unexplained cluster of patients (ie, wrong season, wrong age, negative tests for influenza). Plague, Q fever, and tularemia can also cause severe respiratory symptoms and pneumonia. An aerosol exposure to staphylococcal enterotoxin B (SEB) can cause the abrupt onset of severe respiratory symptoms. As usual, common causes of pneumonia must be excluded in febrile patients who progress to respiratory distress. The lesions of cutaneous anthrax must be differentiated from those associated with brown recluse spider bites, which may or may not be painful and produce an eschar, as well as the usually painful lesions associated with staphylococcal or streptococcal skin infections, ulceroglandular tularemia, plague, herpetic involvement of an extremity, and orf. Although cat scratch disease usually causes significant lymphadenitis, a pustular lesion may or may not be recalled.
Diagnostic Tests: A widened mediastinum on chest x-ray or CT is highly suggestive of pulmonary anthrax; pleural fluid may also be evident. In pulmonary anthrax, Bacillus anthracis bacilli (not spores) or genetic material may be detectable 2-3 days postexposure (and sometimes later) by Gram stain, routine culture, or PCR of blood, buffy coat, or pleural fluid. PCR or ELISA may sometimes detect protective antigen in serum. Organisms are not typically seen in the sputum since pneumonia is rare. Hemorrhagic meningitis is common and organisms may be identified in CSF. In cutaneous anthrax the organisms can be detected by Gram stain and culture of aspirates from the lesion, but are rarely in blood. Rectal swabs are only used if gastrointestinal anthrax is suspected. The bacilli are not highly infectious, and the spores, which are, are not found within the body unless it is open to ambient air.
Specimen Submission: All specimens must be triple contained in an approved shipping container and have biohazard labels. Before transport is arranged, the receiving laboratory must be alerted prior to transport by calling (800) 252-8239 ("press 1"). Newly available diagnostic tests may be discussed at that time. There is no specific hazard to personnel handling specimens unless they contain spores. Specimens must be accompanied by a Specimen Submission Form and submitted to the Texas Department of State Health Services Laboratory, 1100 West 49th Street, Austin, TX 78756.
Additional Tests: Neutrophilic leukocytosis is often revealed upon laboratory evaluation. Pleural and cerebrospinal fluids may be hemorrhagic. Pleural effusions with or without infiltrates may be evident on chest x-ray.