This patient likely has been exposed to anthrax and should be treated with ciprofloxacin. Although this woman's cutaneous lesion may be a methicillin-resistant Staphylococcus aureus furuncle resulting from contact with her infected husband, the distinctive “coal-like” black eschar, together with similar lesions on two coworkers, requires that anthrax be considered in the differential diagnosis. Oral monotherapy with ciprofloxacin, levofloxacin, moxifloxacin, or doxycycline is recommended as treatment of uncomplicated cutaneous anthrax. Uncomplicated cutaneous anthrax is defined as the absence of systemic symptoms and involvement of the head or neck in the absence of extensive swelling. Moreover, suspicion of any bioterrorism event must immediately be reported to local health authorities.

The addition of one or two preferably bactericidal antibiotic agents is indicated for treating anthrax when systemic disease is clinically suspected or confirmed. Because this patient does not have systemic disease, doxycycline, imipenem, and rifampin are not necessary.

Trimethoprim-sulfamethoxazole (TMP-SMX) is an appropriate antibiotic for treating most methicillin-resistant S. aureus soft tissue infections, but TMP-SMX is not adequate treatment for anthrax because it has unreliable activity.

In cases of suspected bioterrorism, deferring treatment until culture and biopsy results are available could have serious adverse consequences. Untreated cutaneous anthrax is associated with an estimated mortality rate of 10% to 20% because of secondary bacteremic spread. Treatment should be initiated as soon as the diagnosis is suspected.