Postexposure prophylaxis of tick-borne relapsing fever: lessons learned from recent outbreaks in Israel

Tick-borne relapsing fever (TBRF) is endemic in Israel. Military activities pose a particular risk for TBRF, and its prevention is based on heightened awareness and risk stratification by active surveillance of tick bites and selective postexposure prophylaxis (PEP) with doxycycline for tick-bitten individuals. We report three outbreaks of TBRF affecting 35 exposed military personnel, with an average recognized tick bite rate of approximately 50% and an attack rate of 25-50%. Of 10 TBRF cases, 20% had no evidence of tick bites and thus restriction of PEP administration to individuals with recognized tick bites contributed to TBRF occurrence. As a result of a revised policy, 24 soldiers (including eight with recognized and 16 with unrecognized tick bites) received antimicrobials following the diagnosis of TBRF among their cohorts, and none of these individuals subsequently developed TBRF. The probability for TBRF among exposed individuals associated with well-established cases of TBRF warrants that prompt doxycycline administration be considered in all individuals who share risk factors, regardless of tick bite status.