Subjective Health Complaints and Exposure to Tick-Borne Infections in Southern Norway.

OBJECTIVES Whether tick-borne infections can cause chronic subjective health complaints is heavily debated. If such a causal connection exists, one would expect to find more health complaints among individuals exposed to tick-borne infections than among non-exposed. In this study, we aimed to assess if exposure to tick-borne infections earlier in life, evaluated by examination of serum for IgG-antibodies to tick-borne microbes, was associated with self-reported somatic symptom load. MATERIALS & METHODS All individuals with residential address in Søgne municipality in southern Norway, aged 18-69 years, were invited to participate in the study. Blood samples were analyzed for IgG-antibodies to different tick-borne microbes, and somatic symptom load was charted by the Patient Health Questionnaire-15 (PHQ-15). RESULTS Out of 7424 invited individuals, 2968 (40.0%) were included in the study. We detected IgG-antibodies to Borrelia burgdorferi sensu lato (Bb) in 22.9% (95% CI 21.4 - 24.4). Bb seropositive individuals reported less frequently moderate to severe somatic symptom load (i.e. PHQ-15 sum score ≥10) than seronegative individuals (12.5% versus 17.7%, difference 5.2% (95% 2.1 - 8.0)). However, when adjusting for several other variables in a multivariable linear regression model, presence of serum IgG-antibodies to Bb was not associated with somatic symptom load. Presence of IgG-antibodies to other tick-borne microbes than Bb, or seropositivity to at least two microbes, were also not associated with somatic symptom load. CONCLUSION Presence of serum IgG-antibodies to tick-borne microbes was not associated with self-reported somatic symptom load.