Prophylactic antimicrobial treatment is not routinely indicated
Background Borrelia burgdorferi, which causes Lyme disease, is transmitted by deer ticks (lxodes dammini) in the northeastern and midwestern United States. Although deer-tick bites are common in areas in which the disease is endemic, there is uncertainty about how to manage the care of persons who are bitten.
Method To assess the risk of infection with B. burgdorferi and the efficacy of prophylactic antimicrobial treatment after a deer-tick bite, we conducted a double-blind, placebo-controlled trial in an area of southeastern Connecticut in which Lyme disease is endemic. Children and adults who had been bitten by deer ticks were randomly assigned to receive either amoxicillin or placebo for 10 days. Subjects were followed for one year for clinical manifestations of Lyme disease. Serum samples obtained at enrollment and six weeks and three months later were tested for antibodies against B. burgdorferi.
Results Of the 387 subjects, 205 (53%) were assigned to receive amoxicillin and 182 (47%) to receive placebo. Of 344 deer ticks submitted and analyzed by the polymerase chain reaction, 15% were infected with B. burgdorferi. Erythema migrans developed in two subjects, both of whom had received placebo. There were no asymptomatic seroconversions and no late manifestations of Lyme disease. The risk of infection with B. burgdorferi in the placebo-treated subjects was 1.2% (95% confidence interval, 0.1 to 4.1 percent), which was not significantly different (P = 0.22) from the risk in the amoxicillin-treated subjects (0 percent; 95%confidence interval, 0 to 1.5%).
Conclusion Even in an area in which Lyme disease is endemic, the risk of infection with B. burgdorferi after a recognized deer-tick bite is so low that prophylactic antimicrobial treatment is not routinely indicated.
Shapiro ED, Gerber MA, Holabird NB, et al. "A controlled trial of antimicrobial prophylaxis for Lyme disease after deer-tick bites”" Dec. 17, 1992 327(25):1769-1773