Laboratory Diagnosis of Babesiosis

Case 1 A 52-year-old asplenic man who lived on Martha’s Vineyard, an island off the coast of Massachusetts, was in remission for Hodgkin disease. One week before hospitalization, he observed a targetoid bruise on the back of his leg after having walked through tall grass fields on the island. He reported intermittent fevers, dyspnea, arthralgia, myalgia, and mild abdominal discomfort. A CBC revealed a WBC count of 6.2 × 103/μL (6.2 × 109/L), with 70% (0.70) neutrophils, 10% (0.10) lymphocytes, and 15% (0.15) monocytes. His hemoglobin value was 14.6 g/dL (146 g/L); platelet count, 138 × 103/μL (138 × 109/L); blood urea nitrogen, 14 mg/dL (5.0 mmol/L); and creatinine, 1.0 mg/dL (88 μmol/L). His liver enzymes were slightly elevated, and there was a mild indirect hyperbilirubinemia. A direct Coomb test was negative. Babesia microti was diagnosed on WrightGiemsa–stained blood smears, with a 2.7% parasitemia. Titers for Babesia IgM (>300) and IgG (128) were high. Babesia microti infection was confirmed by polymerase chain reaction (PCR). Serologic test results for Lyme disease were also positive. The patient was treated with clindamycin, quinine, and doxycycline in addition to receiving supportive measures. He made a slow recovery and was discharged from the hospital 8 days after admission.