Estimated incidence of erythema migrans in five regions of France and ecological correlations with environmental characteristics.

BACKGROUND

While several studies conducted on Lyme borreliosis (LB) risk in the United States showed an association with environmental characteristics, most of European studies considered solely the effect of climate characteristics.

OBJECTIVES

The aims of this study were to estimate incidence of erythema migrans (EM) in five regions of France and to analyze associations with several environmental characteristics of the place of residence.

METHODS

LB surveillance networks of general practitioners (GPs) were set up for a period of 2 years in five regions of France. Participating GPs reported all patients with EM during the study period. Data were pooled according to a standardized EM case definition. For each area with a participating GP, age-standardized incidence rates and ratios were estimated. Associations with altitude, indicators of landscape composition, and indicators of landscape configuration were tested with multivariate Poisson regression.

RESULTS

Standardized estimated incidence rates of EM per 10(5) person-years were 8.8 [95% confidence interval (CI)=7.9-9.7] in Aquitaine, 40.0 (95% CI 36.4-43.6) in Limousin, 76.0 (95% CI 72.9-79.1) in the three participating départements of Rhône-Alpes, 46.1 (95% CI 43.0-49.2) in Franche-Comté, and 87.7 (95% CI 84.6-90.8) in Alsace. In multivariate analysis, age-adjusted incidence rates increased with the altitude (p<0.0001) and decreased with forest patch density (p<0.0001).

CONCLUSION

The marked variations in EM risk among the five regions were partly related to differences in landscape and environmental characteristics. The latter may point out potential risk areas and provide information for targeting preventive actions.