Neutropenia in Congenital and Adult Babesiosis.

Objectives: Anemia and thrombocytopenia are expected hematologic abnormalities in patients with acute babesiosis, whereas neutropenia (defined as an absolute neutrophil count of <= 1,800 neutrophils/mu L for adults and <1,200 neutrophils/mu L for infants) is not usually considered a feature of this infection. We studied the frequency with which neutropenia occurs in congenital and adult cases of babesiosis. Methods: The frequency of neutropenia in cases of congenital babesiosis was determined based on a literature review and on the findings in an unreported case. The frequency of neutropenia in adult patients was assessed based on a review of the medical records of 51 patients who were diagnosed with babesiosis between 2010 and 2013 at two medical centers in the Northeastern United States. Results: Four (80%; 95% confidence interval [CI], 36%-98%) of five infants with congenital babesiosis whose neutrophil count was reported were neutropenic. Among 51 adult cases with babesiosis, 11 (22%; 95% CI, 12%-35%) were neutropenic on clinical presentation, and seven others developed neutropenia over the next 1 to 21 days. Thus, a total of 18 (35%; 95% CI, 24%-49%) of the adult patients with babesiosis had neutropenia. Conclusions: Neutropenia appears to be a common finding in infants with congenital babesiosis and is also observed not infrequently in adults with this infection.