Prevalence of antibodies to Borrelia burgdorferi in forestry workers and blood donors from the same region in Switzerland.

Sera from 259 forestry workers and 100 blood donors in the Canton of Solothurn, Switzerland, were tested for IgG antibodies to Borrelia burgdorferi in two EIAs using as antigen either sonic extract of whole organisms or purified flagella. Applying a 95% specific cut-off value based on results in the sera of 100 blood donors, 86 (33%) and 91 (35%) of the forestry workers respectively showed an elevated specific IgG level in the two EIAs. None of the 259 forestry workers had clinical signs of active infection at the time blood was taken, and only nine could recall experiencing erythema-migrans-like skin lesions within the last ten years. Thus, asymptomatic infections must be frequent. Elevated specific antibody levels increased significantly with the age of the forestry workers (p less than 0.0001) and the duration of occupational exposure to ticks (p = 0.0001). Thus serological results in individuals with high exposure to ticks must be interpreted with caution in view of the high a priori prevalence of antibodies to Borrelia burgdorferi in such persons. The prevalence of antibody to the Borrelia burgdorferi flagellum in a control population not selected for tick exposure, in this case blood donors, seems to be independent of geographical origin.