Lyme disease — infection with the tickborne spirochete Borrelia burgdorferi — is becoming more common, and its geographic zone is enlarging. The infection has protean manifestations and has been blamed for chronic symptoms of arthritis and fatigue. The most common initial symptom is erythema migrans (EM), a target-like lesion. Some patients, despite appropriate antibiotic treatment, experience recurrent EM. Distinguishing reinfection from relapse in these individuals can be difficult, and the issue remains controversial.
To explore this matter, researchers compared B. burgdorferi isolates from the skin or blood of adults with recurrent EM (17 patients, 22 paired consecutive episodes). All patients were treated with standard courses of antibiotics during each episode, with subsequent resolution of lesions.
Molecular typing of the isolated strains of B. burgdorferi, including analysis of the gene governing an outer-surface protein, revealed that in all of the paired EM episodes, the two episodes were associated with different strains. All repeat episodes were due to reinfection rather than relapse.
Comment: As noted by an editorialist, this study adds to the evidence that in antibiotic-treated patients, recurrent EM is caused by reinfection rather than by relapse of the original infection. The findings offer no real surprises: EM generally appears days to weeks after the offending tick bite. However, many patients with proven Lyme disease never experience (or notice) EM, and this study does not resolve the question of relapse or new infection in individuals with recurrent systemic symptoms.