Purple plaque on foot after swim in river

A previously healthy 45-year-old white woman was transferred from an external health-care facility with vomiting, abdominal pain, and painful lesions on her foot that had failed to improve despite 24 hours of broad-spectrum antibiotics; doxycycline had been started just before the transfer.

On arrival, the patient was experiencing occasional chills and was found to be febrile, mildly tachycardic, and tachypneic. Examination ...