Paradigm Burgenland:: Risk of Borrelia burgdorferi sensu lato infection indicated by variable seroprevalence rates in hunters

Background: This study concerns the prevalence of antibodies against B. burgdorferi sensu lato as an indicator of previous borrelial infection among hunters, a group of occupationally exposed persons. In order to define associated risk factors and preparing data for future comparisons, a study was performed in the eight districts of Burgenland, the most eastern state of Austria. Methods: Blood samples of 1214 men (median age 51 years, range 18 to 89 years) and 39 women (median age 44 years, range 21 to 69 years) were collected during autumn 2002 and winter 2003. Demographic data regarding age, sex, profession, residence, duration of employment (hunters), hunting-ground, animals in the environment, and history of tick bite were obtained by a questionnaire. A two-step testing strategy was used in which sera were screened for antibodies against B. burgdorferi sensu lato by a commercially available recombinant enzyme-linked immunosorbent assay (Biotest Anti-Borrelia IgG ELISA; Biotest AG, Dreieich, Germany). Reactive sera were then subjected to immuno blot testing (recomBlot Borrelia; Mikrogen, Munich, Germany) for confirmation of specificity. Results: A total of 673 (54%) sera tested positive for IgG antibodies to Borrelia burgdorferi sensu lato: 663 (55%) men and 10 (26%) women. Seropositivity was clearly related to age and duration of hunting activity; it was 33% among persons younger than 29 years and 83% in those older than 70 years. Further, there was also a difference in the distribution of seroprevalence within the districts; the highest was found in hunters from the most southern district of Burgenland, Jennersdorf, (69%) and the lowest was noticed in the most northern district, Neusiedl (39%). Conclusions: We found an overall seroprevalence of 54% in asymptomatic hunters of Burgenland. Infectious risk exists in the entire state but the prevalence rate differs in the various districts indicating a variable risk which peaks in the south. The nearly linear increase of seroprevalence with age and duration of hunting activity reflects repeated tick exposure.