Increased incidence of Lyme borreliosis in southern Sweden following mild winters and during warm, humid summers

  • L. BennetEmail author
  • A. Halling
  • J. Berglund


The aim of the present study was to investigate the long-term incidence rate of Lyme borreliosis and, additionally, to determine whether a correlation exists between climatic factors and summer-season variations in the incidence of Lyme borreliosis. Climatic variability acts directly on tick population dynamics and indirectly on human exposure to Lyme borreliosis spirochetes. In this study, conducted in primary healthcare clinics in southeastern Sweden, electronic patient records from 1997–2003 were searched for those that fulfilled the criteria for erythema migrans. Using a multilevel Poisson regression model, the influence of various climatic factors on the summer-season variations in the incidence of erythema migrans were studied. The mean annual incidence rate was 464 cases of erythema migrans per 100,000 inhabitants. The incidence was significantly higher in women than in men, 505 and 423 cases per 100,000 inhabitants, respectively (p<0.001). The summer-season variations in the erythema migrans incidence rate correlated with the monthly mean summer temperatures (incidence rate ratio 1.12; p<0.001), the number of winter days with temperatures below 0°C (incidence rate ratio 0.97; p<0.001), the monthly mean summer precipitation (incidence rate ratio 0.92; p<0.05), and the number of summer days with relative humidity above 86% (incidence rate ratio 1.04; p<0.05). In conclusion, Lyme borreliosis is highly endemic in southeastern Sweden. The climate in this area, which is favourable not only for human tick exposure but also for the abundance of host-seeking ticks, influences the summer-season variations in the incidence of Lyme borreliosis.


Incidence Rate Ratio Electronic Patient Record Mild Winter Lyme Borreliosis Erythema Migrans 
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This study was funded by grants from the county councils of Blekinge and Skåne. We thank Hans Alexandersson and Marcus Flarup at the Swedish Meteorological and Hydrological Institute for providing us with climate information and Desirée Clemedtsson at the Clinic for Infectious and Skin Diseases at the County Hospital in Karlskrona and the primary healthcare system administrators at the healthcare centres in the Blekinge County for providing us with electronic patient records.


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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  1. 1.Department of Clinical Sciences, General Practice/Family MedicineUniversity Hospital of Malmö, Lund UniversityMalmöSweden
  2. 2.Blekinge FoU-enhetKarlshamnSweden
  3. 3.School of Health ScienceBlekinge Institute of TechnologyKarlskronaSweden

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