Northeastern States See Dramatic Rise in Babesiosis Cases

March 21, 2023

The incidence of babesiosis has increased exponentially in the U.S. Northeast from 2011 to 2019, particularly in Maine, New Hampshire and Vermont, which the U.S. Centers for Disease Control and Prevention (CDC) now considers endemic areas for the tick-borne infection.

Babesia microti, the pathogen species primarily responsible for babesiosis, is carried by black-legged ticks, Ixodes scapularis. Although generally asymptomatic, Babesia infection can be fatal in some cases.

“Reported case counts in Maine, New Hampshire and Vermont were similar to or higher than those in states previously identified as having endemic babesiosis, and annual incidences in these states have increased significantly,” according to a new report published in the March 17 issue of the Morbidity and Mortality Weekly Report.

Vermont experienced a 1,602% increase in cases from 2011 to 2019, up from two cases in 2011 to 34 in 2019. In Maine, the number of new cases jumped from nine cases in 2011 to 138 cases in 2019, a 1,422% rate increase. Reported new cases in New Hampshire increased by 372%, up from 13 to 63.

Babesiosis is already considered to be endemic in several states in the Midwest and Northeast. While not previously considered to have endemic transmission, Maine, New Hampshire and Vermont should now be considered endemic regions, according to the report.

Babesia infection risk in these three states is now comparable to risk in Northeastern and Midwestern states where babesiosis is endemic. CDC previously considered babesiosis to be endemic and reportable in Connecticut, Massachusetts, Minnesota, New Jersey, New York, Rhode Island and Wisconsin. FDA’s 2019 Babesia guidance recommends testing of blood donors for Babesia infection in 14 states – Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia, Wisconsin and the District of Columbia.

In states where testing is not required, FDA recommends addressing the risk of transfusion-transmission of Babesia by including a question on the donor history questionnaire (DHQ), “Have you ever had a positive test result for Babesia?” In addition, tick-borne and transfusion-transmission risks should be evaluated in states that border those considered endemic for “the evaluation and evolution of babesiosis blood screening policy.”

AABB previously provided members with a Babesia toolkit, which includes information regarding the DHQ v2.0. The current donor screening criteria are included in AABB’s draft DHQ v4.0 System of Documents, which is set to be submitted to FDA for review and acceptance.

The new report from CDC is based on data from a national babesiosis surveillance system, including 41 states where babesiosis was reportable from 2011 to 2019, and is the first comprehensive national surveillance assessment and multistate analysis of babesiosis over time.

Symptoms of babesiosis are non-specific and include fever, muscle, joint pain and headache. Health care providers should be aware of Babesia infection risk in states with endemic disease and bordering states. In addition, people in endemic states who spend time outdoors should be advised to practice tick bite prevention.