Prevalence and incidence of Lyme borreliosis among Slovene forestry workers during the period of tick activity

OBJECTIVES: To establish the prevalence and incidence of symptomatic and asymptomatic infection with Borrelia burgdorferi sensu lato during the period of tick activity, to compare the risk of infection with B. burgdorferi s.l. for forestry workers and indoor workers in Slovenia, and to compare the outcome of an in-house immunofluorescent assay (IFA) and a commercially available enzyme-linked immunosorbent assay (ELISA). METHODS: The study included 122 forestry workers; the control group consisted of 93 indoor workers. All participants were examined twice in 2002: before the beginning of tick activity (March) and at the end of tick activity (November). At each examination, principal demographic and epidemiological data were collected and a blood sample taken for serological analysis. Specific IgM and IgG antibodies against B. burgdorferi s.l. in the paired sera were determined with an in-house IFA and a commercially available ELISA flagellin test (DAKO). RESULTS: 9.8% of the forestry workers and 4.3% of the indoor workers tested positive for IgG with the IFA (p = 0.26); 23.8% of the forestry workers and 9.7% of the indoor workers tested positive for IgG with the ELISA (p = 0.02). During the study period the incidence of symptomatic Lyme borreliosis was 2.3% and the rate of IgG and/or IgM seroconversion of 10.2% was the same with both tests. CONCLUSIONS: The seroprevalence of antibodies against B. burgdorferi s.l. among the Slovene forestry workers was greater than among the indoor workers, but the difference between the two groups was not significant when the IFA was used. The incidence of Lyme borreliosis during the period of tick activity was lower than we expected, with a large proportion of seroconversions being asymptomatic.