One year follow-up study to assess the prevalence and incidence of Lyme borreliosis among Dutch forestry workers.

A one-year serological and clinical follow-up study was conducted to assess the prevalence and incidence of asymptomatic and symptomatic infection with Borrelia burgdorferi among 151 Dutch forestry workers. The prevalence of antibodies to Borrelia burgdorferi among the forestry workers and among office employees as control group was compared. Antibodies to Borrelia burgdorferi were detected by enzyme immunoassay. Forestry workers were examined physically at the start of the study. Clinical follow-up of forestry workers whose first blood sample was positive and of persons showing seroconversion was done by telephone interview. If Lyme borreliosis was suspected, clinical and laboratory data were obtained. The seroprevalence was significantly higher among forestry workers (28%) than among controls (5%). Of 127 forestry workers who were examined, 7 (18%) of the 39 seropositive persons but none of the seronegative persons had a history of Lyme borreliosis. None of 32 asymptomatic seropositive forestry workers had developed Lyme borreliosis one year later. The incidence of infection with Borrelia burgdorferi as demonstrated by seroconversion among 95 initially seronegative forestry workers was 5%. None of them had Lyme borreliosis. Infection with Borrelia burgdorferi among forestry workers is frequent but seems to take a benign course.