Erythema Migrans in Primary Health Care

Abstract: Lyme borreliosis (LB) is the most common vector-borne disease in the northern hemisphere, and southern Sweden is a highly endemic area. In over 70% of the cases, LB is represented by the non-disseminated cutaneous form erythema migrans (EM). This thesis has its focus on EM from a primary health care perspective in southern Sweden, including aspects on epidemiology, the clinical picture, gender differences and the climate.

In paper III, an annual mean incidence rate over 460 cases of EM per 100,000 inhabitants was found in the county of Blekinge. Over 98% of the cases were treated in primary health care and almost every second case occurred during the vacation months of July and August. In paper I, individuals in southern Sweden treated and recovered from EM were followed during a period of 5 years. Annually, 1% were 'reinfected', i.e. had a new infection with LB during the follow-up. This is significantly higher than the prevalence of LB in the area in 1992-1993 of 0.07% (p < 0.001), indicating that individuals with a former infection are at a higher risk of LB.

In paper IV studying patients with EM, where genospecies were confirmed by PCR, 74% of the patients were infected with B. afzelii and 26% were infected with B. garinii. B. garinii seemed to cause more intense local and systemic inflammatory reactions than B. afzelii. Totally, 45% (38/85) of the lesions were annular, 46% (39/85) were non-annular and 9% (8/85) were atypical. An interaction between gender and genospecies was found that has not been described before. Men to a higher extent than women developed annular EM while women more often developed non-annular EM, if infected with B. afzelii. Surprisingly, time duration from tick bite to diagnosis was not found to have an effect on the clinical appearance of the EM.

In paper II, antibiotic treatment of EM with pcV and doxycycline was found to be highly effective and no cases of disseminated LB were found in patients followed for 5 years.

The incidence rate of EM was significantly higher in women than men (506/100,000 vs 423/100,000 p < 0.001) and especially women over 50 years were affected (paper III). Additionally, significantly more women than men were reinfected, 6% and 1%, respectively (p < 0.01). All infected women were over the age of 44 years and they were tick-bitten to the same extent as the men (paper I). Immunological differences might have an impact on, and explain, the observed gender differences.

The seasonal incidence rates of EM varied considerably. Different climate factors were found to influence the EM incidence rates (paper III).