A retrospective cohort study of 193,260 people in the U.S. who were tested for tick-borne diseases found that 5% were seropositive for Borrelia burgdorferi, the bacterium that causes Lyme disease. Among those, 29.5% also tested positive for antibodies to at least one of three other tick-borne pathogens: Anaplasma phagocytophilum, Babesia microti, or an Ehrlichia species. The results appeared in a "JAMA Network Open" research letter.
Co-seropositivity varied by geography. In the Northeast, 31.1% of B. burgdorferi-positive patients also had antibodies to another pathogen, while the Midwest and West had rates of 16.6% and 13.6%, respectively. Across the entire tested population, 6.7% were positive for at least one non-Lyme pathogen. The authors note that tick species are expanding beyond their traditional ranges, making regional assumptions less dependable.
Study co-author Ross Boyce of the University of North Carolina at Chapel Hill said clinicians may be underprepared for this complexity. Even when symptoms are typical of Lyme disease or the Lyme test is positive, he said, other pathogens should be considered. The distinction matters for treatment: doxycycline, used for Lyme disease, also covers anaplasmosis but is not effective against babesiosis. Boyce cautioned, however, that positive antibody tests do not necessarily mean active co-infection, since exposures could have occurred at different times.
The study had limitations, including a lack of information about the clinical indications for testing and whether symptoms were acute or chronic. The analysis drew on Quest Diagnostics serological panel results from January 2021 through December 2025.