Seroprevalence of anti-Borrelia IgG antibodies in blood donors in Sweden.

INTRODUCTION The aim of this study was to investigate the seroprevalence of IgG antibodies to Borrelia burgdorferi sensu lato (Bbsl) in the Swedish population, an indication of ongoing or previous Bbsl infection, by assessing seroprevalence among healthy blood donors covering all administrative regions.

Methods

Sera from 2058 healthy adult blood donors were collected during 2024 in Sweden's 21 administrative regions. Anti-Bbsl IgG antibodies were detected in sera using Liaison Borrelia IgG VlsE kit as a screening test and Anti-Borrelia EUROLINE-RN-AT IgG as a confirmatory test.

Results

The analyses revealed an overall seroprevalence of 16% with significant differences between age groups, sexes and geographical regions. The seroprevalence in females was 11% compared to 21% in males (p < 0.0001). Seroprevalence increased with age, from 8% in the youngest age group (18-29 years) to 29% in the oldest age group (60 years and above) (p < 0.0001). The seroprevalence was higher in the southern and central parts of the country (17-19%), compared to the northern part (5%) (p < 0.0001). Among the 21 Swedish administrative regions, the seroprevalence ranged from 0% in Region Norrbotten to 27% in Region Gotland.

Conclusions

Except for the Northern part of Sweden, the seroprevalence of antibodies to Bbsl indicates that a substantial proportion of the population has been infected with Bbsl. The seroprevalence varies with sex and across different age groups, which should be taken into consideration in the interpretation of serological test results for the diagnosis of LB. Furthermore, the outcomes of the study indicate that the LB disease burden may be substantial in Sweden.