Incidence and antibiotic treatment of erythema migrans in Norway 2005-2009

The first stage of Lyme borreliosis (LB) is mainly the typical skin lesion, erythema migrans (EM), which is estimated to comprise 80-90% of all LB cases. However, the reporting of, and the actual incidence of LB varies throughout Europe. Studies from Sweden and Holland have found EM incidences varying from 53 to 464 EM/100,000 inhabitants/year. Under-reporting of LB is common and a coefficient of three to reach a realistic estimate is suggested. In Norway, it is mandatory to report only the second and third LB stages to the National Institute of Public Health. To find the Norwegian incidence of EM, we extracted data from the electronic medical records of regular general practitioners and out-of-hours services in the four counties with the highest rates of registered LB in the 5 years from 2005 to 2009. We found an EM incidence of 448 EM/100,000 inhabitants/year in these counties, which yields a national incidence of 148 EM/100,000 inhabitants/year. Our findings show that solitary EMs comprised almost 96% of the total LB incidence in Norway. Older females have the highest rates of EM. Phenoxymethylpenicillin is the most commonly used drug to treat EM in Norway, which complies with the national guidelines for antibiotic use. Antibody tests are performed in 15% of cases. Less than 1% of patients are referred to secondary care. The study also shows a high number of patients seeking care for tick bites without signs of infection and there is an overuse of antibiotics in these patients.