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A 59-year-old man presented to The Toronto Hospital on July 27, 1997, because of fever. His travel history included a trip to Nantucket, Mass., 6 weeks before presentation and to Southeast Asia 7 months earlier. There was no history of rural travel on either trip. The past medical history was noncontributory. The patient had not undergone splenectomy, nor had he ever received a blood transfusion.
The patient had been well until June 21, 1997, when he noticed a small "pinhead" lesion on his left biceps, which he removed. He subsequently experienced fever and spreading erythema (to 5 cm in diameter) surrounding the site of the lesion; the erythema subsequently resolved. He was then well until July 21, when the fever returned, along with rigors, extreme fatigue, headache, myalgia, vomiting and drenching night sweats. On July 22 he saw his family physician, who diagnosed a viral infection. On presentation to the hospital 5 days later, the patient was febrile (temperature 38.8C) and pale and appeared unwell. He had tachycardia (130 beats/minute), splenomegaly and scattered petechiae. Laboratory investigations revealed anemia, marked thrombocytopenia and a bleeding diathesis (Table 1).
His fever and travel to Southeast Asia suggested malaria; smears were ordered, and the results were initially interpreted as positive for Plasmodium falciparum (4% parasitemia). However, a senior technologist reviewed the smears a few hours later and correctly identified the organisms as trophozoites of Babesia.
Given the severity of his illness and the preceding rash consistent with erythema migrans, there were concerns about coinfection with additional tick-borne agents. Serologic testing for Lyme disease was performed, and the results of both enzymelinked immunosorbent assay and Western blotting for [gM were positive, which indicated recent infection. Serologic testing for human monocytic ehrlichiosis (Ehrlich. ia chaffeensis) by immunofluoresence assay, performed at the Ontario Provincial Laboratory, was negative at 1:64 dilution. Polymerase chain reaction assays for human granulocytic and monocytic ehrlichiosis were performed in the laboratory of one of the authors (K.C.K.); the results were negative.'
The patient was treated with quinine (600 mg three times daily) and clindamycin (600 mg three times daily) for 7 days for the babesiosis and doxycycline (100 mg twice a day) for 21 days for the Lyme disease. The response was prompt, and smear testing...