Patients with Erythema Migrans: Characterizing the Impact of Initiation of Antibiotic Therapy Prior to Study Enrollment.

Erythema migrans is the most common clinical manifestation of Lyme disease, with concomitant subjective symptoms occurring in ∼65% of cases in the United States. We evaluated the impact of having been started on antibiotic treatment before study enrollment on 12 particular symptoms for 38 subjects with erythema migrans versus 52 untreated subjects. There were no significant differences in the frequency of having at least one symptom or in the symptom severity score on study entry. However, the frequency of having at least one symptom was significantly greater for those who had received <7 days of antibiotic treatment than for those who had been treated for ≥7 days (23/24 [95.8%] versus 8/14 [57.1%], P = 0.006). In addition, the percentage of subjects who were males was significantly lower among the group on treatment than among the untreated study subjects (13/38 [34.2%] versus 34/52 [65.4%], P = 0.005). In conclusion, based on these findings, combining untreated and treated groups of patients with erythema migrans for research study analyses may have limitations and, depending on the study objectives, might not be preferred. Additional studies are warranted to better understand the day-to-day impact of antibiotic treatment on the presence, type, and severity of symptoms in patients with early Lyme disease.