Severe Babesiosis in a Patient Treated With a Tumor Necrosis Factor Antagonist

To the Editor—A 57-year-old woman from Cape Cod presented to our facility with fever and a syncopal episode. She reported 1 week of fatigue before her evaluation. On examination, she was febrile (38.6 C) but otherwise appeared well, with a positive Castell’s sign and palpable spleen tip. Her medical history was significant for Crohn’s disease treated with infliximab, with the most recent dose administered 6 weeks before presentation. She did not report smoking or alcohol consumption, denied any travel history, and worked in a local office. Blood work on admission revealed a white blood cell count of 6.8 3 10/lL with a normal differential, a hemoglobin level of 11.5 g/dL, a hematocrit of 34.8%, and a platelet count of 88 3 10/lL. The patient’s serum lactate dehydrogenase level was elevated (659 U/L), her creatinine level was normal (0.81 mg/dL), and her aspartate aminotransferase and alanine aminotransferase levels were slightly elevated (54 and 39 U/L, respectively). Intraerythrocytic parasites were visualized on a blood film and confirmed via light microscopy as babesia with 14.1% parasitemia. The patient was initially treated with azithromycin (500 mg daily) and atovaquone (750 mg twice daily) for babesiosis, in addition to empiric therapy with doxycycline (100 mg twice daily) for possible coinfection with Borrelia, Ehrlichia, and Anaplasma. Doxycycline was discontinued on hospital day 2, after results were negative for Ehrlichia (polymerase chain reaction) and Borrelia (serology). The patient appeared well despite parasitemia of 15% for 4 days, and her treatment was briefly switched to quinine and clindamycin (650 and 600 mg, respectively, each 3 times daily on hospital day 4). Atovaquone and azithromycin treatment were restarted on hospital day 5, when her parasitemia declined to 10%. Parasitemia was undetectable by microscopy on hospital day 7. The patient was treated for 2 additional weeks with atovaquone and azithromycin after her parasitemia became undetectable, for a total of 3 weeks of therapy. She was well at follow-up appointments 3 and 12 weeks after hospital discharge, with blood work revealing absent parasitemia and normalizing anemia and liver function values. To our knowledge, this is the second case of babesiosis reported in a patient treated with an anti–tumor necrosis factor (TNF) agent. The first report involved a patient in Wisconsin with underlying rheumatoid arthritis treated with etanercept (50 mg weekly) and prednisone (5 mg daily) in whom Babesia