Transfusion-transmitted and community-acquired babesiosis in New York, 2004 to 2015.

BACKGROUND: Babesiosis is a potentially life-threatening zoonotic infection most frequently caused by the intraerythrocytic parasite Babesia microti. The pathogen is usually tickborne, but may also be transfusion or vertically transmitted. Healthy persons, including blood donors, may be asymptomatic and unaware they are infected. Immunocompromised patients are at increased risk for symptomatic disease. STUDY DESIGN AND METHODS: All reported community-acquired babesiosis cases in New York from 2004 to 2015 were evaluated, enumerated, and characterized. All potential transfusion-transmitted babesiosis (TTB) cases reported through one or more of three public health surveillance systems were investigated to determine the likelihood of transfusion transmission. In addition, host-seeking ticks were actively collected in public parks and other likely sites of human exposure to B. microti. RESULTS: From 2004 to 2015, a total of 3799 cases of babesiosis were found; 55 (1.4%) of these were linked to transfusion. The incidence of both community-acquired babesiosis and TTB increased significantly during the 12-year study period. The geographic range of both ticks and tickborne infections also expanded. Among TTB cases, 95% of recipients had at least one risk factor for symptomatic disease. Implicated donors resided in five states, including in 10 New York counties. More than half of implicated donors resided in counties known to be B. microti endemic. CONCLUSION: The increasing incidence of TTB correlated with increases in community-acquired babesiosis and infection of ticks with B. microti. Surveillance of ticks and community-acquired cases may aid identification of emerging areas at risk for Babesia transfusion transmission.