Epidemiology and clinical manifestations of Lyme borreliosis.

Epidemiological and clinical characteristics of Lyme borreliosis (LB) in Sweden are described through a one year surveillance-study. The findings differed only marginally when compared to studies from the United States indicating similar clinical presentation of the disease. Incidence was 69/100.000/year with large variation between counties (26-160/100.000/year) and concentration of the disease to the south-eastern coast of Sweden. The incidence varied according to age in a bimodal pattern with the highest rates among those aged 5-9 or above 45 years. The most frequent manifestation was erythema migrans (EM; 77%), followed by neuroborreliosis (16%), arthritis (LA; 7%), acrodermatitis (3%), borrelial lymphocytoma (3%), and carditis (0.5%). Seasonal distribution showed tick-bites to be most frequent in July, whereas most cases of erythema migrans occured in August and other manifestations peaked in September. A population (n=540), from an area with the highest endemicity in the region, was followed during a three year period and studied with regard to the clinical manifestations and antibody prevalence of LB. At start 90/480 (19%) had IgG antibodies to Borrelia burgdorferi s.l. Subclinical infection dominated; 18 (4%) had a medical history of LB but late manifestations of the disease were found in several of the seropositive subjects when further examined. Based on musculoskeletal symptoms in 34/90 (38%) seropositive and in 48/390 (12%) of seronegative subjects (p<0.001), LA was identified in 11, a prevalence of 2.3% (95% CI 1.0-3.6). In 301 of the individulas, annual seroconversion were seen in 9.7%, 7.3%, and 4.8%, respectively. A total of 34 individuals developed a physician diagnosed manifestation of LB but most individuals had a subclinical infection. Most seropositive remained positive with stationary antibodylevels during the whole follow-up period and at the latest follow-up 101/301 (34%) had IgG antibodies to B. burgdorferi s.l. In rheumatological practice 5% of new referrals in a highly endemic county were found to have potential curable LA. Based on the findings of LA in all studied populations, that condition with its specific clinical presentation was identified as an important manifestation also in Sweden.