Among 193,260 Americans tested for tick-borne illness over five years, 29.5% of the people who tested positive for the Lyme bacterium also carried antibodies to a second tick-borne pathogen, according to a cohort study published September 18, 2026, in JAMA Network Open. Among people who tested negative for Lyme, only 5.5% did.
That gap matters for one practical reason. Doxycycline, the first-line antibiotic for Lyme, works against two of the other pathogens here but does nothing against the third, Babesia, a malaria-like parasite that needs different drugs. So if a tick bite sent you for Lyme testing, it is worth asking your doctor about testing for babesiosis, anaplasmosis and ehrlichiosis too.
Antibodies are not proof of an active infection, and the authors say so directly. A positive result is a reason to talk to a doctor, not a reason to ask for treatment. Whether an old infection can still do damage long after it clears is a separate question, and one large study of the shingles vaccine put a number on it.
Key takeaways
- Lyme-positive patients were about 4.5 times as likely as Lyme-negative patients to carry antibodies to another tick-borne pathogen (29.5% versus 5.5%).
- Babesia was the most common of those other pathogens, and doxycycline does not treat it.
- These are antibody tests. They show past exposure, not necessarily a current infection.
What the study found
Researchers queried the Quest Diagnostics test database for people who had a tick-borne disease serology panel between January 2021 and December 2025. The cohort was 193,260 people, 56.3% female, median age 51. Most, 70.6%, lived in the Northeast.
Antibodies to Borrelia burgdorferi, the Lyme bacterium, showed up in 5.0%. Babesia microti came in at 3.4%, Anaplasma phagocytophilum at 3.1% and Ehrlichia species at 1.0%.
Then the main comparison: 29.5% of Lyme-positive people were also positive for at least one other tick-borne pathogen, versus 5.5% of Lyme-negative people. That is about 24 more people per 100 carrying a second set of antibodies. Put as a ratio, Lyme-positive patients were roughly 4.5 times as likely to be positive for something else, very likely between 4.3 and 4.6 times (seropositivity ratio 4.46; 95% CI, 4.30 to 4.63). There is less than a 1 in 1,000 chance a gap this size is coincidence (P < .001).
Region mattered. In the Northeast, 31.1% of Lyme-positive people were also positive for a non-Lyme pathogen, compared with 13.6% to 16.6% in other regions.
Dr. Kumar’s take
The number is interesting. The drug list is what actually changes anything.
Doxycycline covers Lyme, anaplasmosis and ehrlichiosis. That is a tidy piece of luck, and it is why one antibiotic has carried so much of tick-borne medicine. Babesia breaks the pattern. It is a parasite, not a bacterium, it lives inside red blood cells more like malaria, and it needs its own medication. It was also the most common non-Lyme finding here, at 3.4%.
That gives an ordinary explanation for a story people tell online all the time: I was treated for Lyme, I finished the antibiotics, and I still feel terrible. One plain possibility is that something else came in on the same tick and never got treated.
Now the part the headline number invites people to skip. Seropositive means your blood carries antibodies, and antibodies can persist for years after an exposure your body already handled. The authors state flatly that coseropositivity does not prove active co-infection, and they note that standard two-tier Lyme testing is less sensitive in early disease. This is a lab database, not a group of examined patients, so nobody here was confirmed sick.
There is a selection effect too. These were people whose doctors already suspected tick-borne disease and ordered a full panel, so the percentages are not the rate in everyone who gets bitten.
What it means for you
Ask whether a full tick-borne panel makes sense for you, particularly in the Northeast. Babesiosis is the one that matters most, because finishing a course of doxycycline does not address it.
If you were treated for Lyme and still feel unwell, that is a conversation to have, not a diagnosis to assume. Lingering symptoms have several possible causes, and an untreated co-infection is one.
And a positive result is not a verdict on its own. Antibodies plus current symptoms are a clinical picture. Antibodies alone may be a record of something your immune system dealt with years ago. Sorting those apart needs a doctor who can examine you.
Prevention still beats all of it, here and nearly everywhere else. How much of serious illness actually traces back to risks you can act on is a question one large US analysis answered. For ticks, the answer is dull: check your skin after tall grass or woods, and get them off early.