Borrelia burgdorferi antibodies in outdoor and indoor workers in south-west Sweden

Two hundred and fifty-three farmers and forest workers and 249 clerks from south-west Sweden were recruited to a cross-sectional seroprevalence study to find out if individuals working outdoors are more prone to acquire Borrelia burgdorferi infection than indoor workers and to find undiagnosed cases of Lyme borreliosis. The participants answered a questionnaire and blood specimens were collected to estimate the prevalence of antibodies to B. burgdorferi in each group. Sera were analysed with an enzyme-linked immunoassay technique to determine IgG antibodies to B. burgdorferi flagellum. The prevalence of B. burgdorferi antibodies was 7.6% in the farmers and forest workers vs. 5.3% in the clerks (adjusted odds ratio [age, sex] = 1.2 [95% confidence interval = 0.5-2.8]). One case of Lyme borreliosis was diagnosed. The positive predictive value of the antibody test was estimated to be 3% in the studied populations. B. burgdorferi infection is of low endemicity in south-west Sweden and is probably not an occupational risk among outdoor workers. Undiagnosed cases of Lyme borreliosis are uncommon. The test used is not acceptable for screening purposes.