Nearly 1 in 3 People With Lyme Disease Bacteria Carry Other Tick-Borne Pathogens

Nearly one-third of people who tested positive for the bacteria that cause Lyme disease also tested positive for other tick-borne pathogens, according to a retrospective cohort study.

Among 193,260 people tested for tick-borne diseases in the U.S., 5% were seropositive for Borrelia burgdorferi, the bacterial species that triggers Lyme disease. Among those B. burgdorferi-positive people, 29.5% also tested positive for at least one of the tick-borne pathogens Anaplasma phagocytophilum, Babesia microti, or an Ehrlichia species.

Geography helped shape multiple-pathogen positivity. In the U.S. Northeast, 31.1% of people positive for B. burgdorferi also tested positive for at least one of those other three pathogens. That rate was nearly double the Midwest’s rate, at 16.6%, and well above the 13.6% rate in the West, the region with the lowest co-seropositivity, Yonghong Li, PhD, of Quest Diagnostics in San Juan Capistrano, California, and colleagues reported in a JAMA Network Open research letter.

“The potential for infections with other pathogens besides Lyme disease is increasing similarly, and I think clinicians are underprepared to deal with that complexity,” study co-author Ross Boyce, MD, of the University of North Carolina at Chapel Hill, told MedPage Today. “Even if the Lyme disease test is positive, or the symptoms are typical of Lyme disease, clinicians certainly need to be thinking about these other pathogens.”

“As a clinician, what you worry about is when there are differences in tick-borne disease treatments,” Boyce said. For example, treating a potential Lyme disease case with doxycycline will also cover anaplasmosis — but the antibiotic isn’t a treatment for babesiosis.

Lyme disease is the nation’s most frequently reported vector-borne disease, but the study researchers found seropositivity rates for the other three tick-borne pathogens weren’t far behind B. burgdorferi‘s 5% rate.

Overall, B. microti antibodies were found in 3.4% of the study’s population, A. phagocytophilum antibodies in 3.1%, and Ehrlichia species antibodies in 1.0%. B. microti infection can cause babesiosis, A. phagocytophilum can lead to anaplasmosis, and Ehrlichia species can cause ehrlichiosis — all with symptoms that overlap those of Lyme disease.

While co-infections can happen, testing positive for multiple tick-borne pathogen antibodies doesn’t mean a person has one, Boyce cautioned. “Some of these people could have been concurrently infected by a single tick, or some of them could have had asynchronous exposure” through multiple tick bites over time, he noted.

Clinicians’ diagnostic challenges also grow as tick species spread beyond their traditional regional homes. The blacklegged (deer) tick transmits B. burgdorferi, A. phagocytophilum, and B. microti, with a traditional range across the eastern U.S., while the Ehrlichia-transmitting lone star tick has covered a slightly more southern range.

However, “the traditional regional wisdom about ‘We don’t have X’ or ‘We don’t have Y’ no longer applies,” Boyce explained. “Within the U.S., it’s getting messier and messier as northern ticks are migrating south, and the ticks that are down here have migrated north.”

The study’s strong correlation between B. burgdorferi and Ehrlichia seropositivity may reflect infections with an Ehrlichia species that can be carried by blacklegged ticks, Boyce noted.

The researchers analyzed tick-borne disease serological panel test results from the Quest Diagnostics database between January 2021 and December 2025. Most of the study population (92.4%) was age 18 years or older, median age was 51 years, 56.3% were female, and 70.6% lived in the Northeast.

Out of those suspected to have Lyme disease and tested, 6.7% overall tested positive for at least one non-Lyme disease pathogen.

Study limitations included a lack of knowledge about what clinical indications led to a test being ordered, as well as no data about whether symptoms were acute or chronic.