Abstract
Background. Estonia is an endemic country of Lyme borreliosis with an especially high prevalence in Saaremaa. Previous studies have shown high antiborrelial antibody levels in populations that spend a significant amount of time outdoors in endemic areas. Although the two-step serological testing has been recommended for Lyme borreliosis in most guidelines, in practice only immunoenzymatic (ELISA) tests are oftren used.
Aim. We aimed (1) to determine the level of anti- Borrelia burgdorferi antibodies (IgG
and IgM) in otherwise healthy hunters; (2) to compare the results of ELISA and immunoblotting in terms of IgM and IgG antibodies; (3) to describe reasons for testing for borreliosis.
Methods. Two studies were carried out in Saaremaa. In 2012, 184 hunters filled in a questionnaire and gave blood samples to measure IgM and IgG antibodies with ELISA. The other study was conducted by general practitioners in 2009. Within that study 181 subjects who had been tested seropositive by ELISA (109 had IgM antibodies and 123 had IgG antibodies) filled in the questionnaire and had their blood samples retested by immunoblotting.
Results. Altogether 86 (46.7%) and 10 (5.4%) hunters were seropositive for IgG and IgM antibodies, respectively. Seropositivity was not related to frequency of visiting forest and/or to number of tick bites in the past 5 years (69%), however, IgG seropositivity was positively correlated with age and with duration of hunting activities.
The mean titres of IgM and IgG were 54.8 (17.1- 219) and 36.8 (17.0- 250.0) in patients tested by GPs, respectively. Comparison of the ELISA and immunoblotting results showed that 26 (23.9%) and 23 (18%), respectively, were false positive by ELISA. The positive predictive value was 76% in testing IgM (95% CI 67-84%) and 81% in testing IgG (95% CI 73-88%). The prevalence oferythema migrans was low and did not correlate with presence of antibodies.
Conclusions. As the background seropositivity of Lyme borreliosis in hunters in Saaremaa is high, antibody testing can support the diagnosis only when typical clinical findings of Lyme borreliosis are present. In the case of low antibody levels, immunoblotting is required to confirm positive ELISA results.