What is the epidemiology of babesiosis in the US?

Updated: Apr 01, 2021
  • Author: Rachel E Strength, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Human babesiosis is endemic in the northeastern coastal region of the United States, particularly Nantucket Island, Martha’s Vineyard, and Cape Cod, Massachusetts; Block Island, Rhode Island; and eastern Long Island, [14] Shelter Island, and Fire Island, New York.  Disease prevalence in Cape Cod, as suggested by antibodies to B. microti, has been reported as 3.7%, whereas on Shelter Island in individuals with a high risk of exposure to ticks, it was 4.4% in June and reached 6.9% by October.

Babesiosis was a reportable condition in 40 out of 50 states in 2018.  Of those, 28 states reported cases of babesiosis during that year. Most (86%) of the 2,161 cases were reported by 7 states: Connecticut, Massachusetts, New Jersey, Rhode Island, New York, Minnesota, and Wisconsin. [5]

The incidence of babesiosis has increased over the past 20 years. [15]  This is thought to be the result of restocking of the deer population, curtailment of hunting, and an increase in outdoor recreational activities; however, the prevalence of this disease is unknown because most infected patients are asymptomatic.

In endemic areas, the organism may also be transmitted by blood transfusion. [3, 16, 17, 18, 19, 20, 21]

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