Bartonella spp. seroprevalence in tick-exposed Swedish patients with persistent symptoms

Background: Bartonella spp. are emerging pathogens transmitted by arthropod vectors, possibly including ticks. We have investigated signs of bartonellosis in Swedish patients with presumed tick-bite exposure and symptom duration of at least 6 months. Methods: Serological testing for Bartonella henselae and Bartonella quintana was performed in 224 patients. Symptoms, tick exposure, evidence of co-infection and previous treatments were evaluated. Seropositive patients were compared to a matched group (twofold larger and negative serology) from the same study cohort. Results: Seroprevalence was 7% for B. henselae and 1% for B. quintana, with one patient testing positive to both agents. Tick bites were reported by 63% of the patients in the seropositive group and 88% in the seronegative group and presumed tick exposure was more common in the seronegative group. Animal contact was equally common in both groups, along with reported symptoms. The most common symptoms were fatigue, muscular symptoms, arthralgia and cognitive symptoms. Exposure to co-infections was evenly distributed in the seropositive and seronegative groups. Conclusions: Antibodies to Bartonella were more common in this cohort of patients than in cohorts of healthy Swedish blood donors in previous studies but lower than those in blood donors from southern Europe. Positive Bartonella serology was not linked to any specific symptom, nor to (suspected) tick-bite exposure.