Increasing Length of the Babesia Season in New England in the Climate Change Era.

In a retrospective cohort of 1130 patients with babesiosis over a period of 31 years, there was a marked expansion of the Babesia season over time, with an increase of 0.33 months per year (CI .27 to .39) in a generalized linear model. The mean number of months with patients developing symptomatic infection with Babesia microti rose from 2.2 before 2000 to 9.2 after 2015. In the climate change era, babesiosis should be considered in the differential diagnosis of patients presenting with fever and anemia outside of peak summer months.