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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.

The true number of industrial accidents followed by absence from work in the Netherlands in 1993 has been estimated by using a capture-recapture approach. A government safety register noted 29,685 cases reported by Dutch companies. The statutory organization that insures employees of the same companies against absence from work for medical reasons (but does not provide special compensation for disability due to accidents at work) noted 19,397 cases for which absence control visits revealed an occupational injury to be the cause of the absence. These two registers showed an overlap of 5,881 matched cases. Assuming them to be independent and capture probability to be homogeneously distributed, the authors obtained a crude estimate of 97,909 accidents. Two methods for correcting this crude estimate are presented. The first method is logistic modeling of the data using age, sex, branch of industry, number of work sites, size of workforce, and seriousness of injury as explanatory variables to allow for heterogeneity in capture probabilities. Applying the model coefficients of these characteristics to the 43,201 distinct cases noted in both registers, we obtained an estimate of 97,524 accidents. Second, knowledge of the reporting and registration procedures utilized by the two sources was used to obtain an estimate of source bias. Errors in recording date of birth and differences between the two registries precluded matching of a number of overlapping cases, accounting for 16.9% overestimation of the true number, corresponding to 83,283 accidents and a government capture rate of 35.6%.

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Abstract. One hundred and fifty-one forestry workers and 151 matched office clerks were compared as to the presence of antibodies against Borrelia burgdorferi, tick-borne encephalitis virus, Puumalavirus and lymphocytic choriomeningitis virus. Their occupational risks of being infected by Borrelia was fourfold and significant, by Puumalavirus and lymphocytic choriomeningitis virus was increased but not significant. No seropositivity has been established against tick-borne encephalitis virus.