Tick-borne relapsing fever in the northwestern United States and southwestern Canada

Records from 182 cases of tick-borne relapsing fever (TBRF) were reviewed. In confirmed cases, there was febrile illness, and spirochetes were identified on peripheral blood preparations, In probable cases, there were clinical features of TBRF and either the same exposure as a confirmed case or serological (indirect fluorescent antibody test and western blotting [WB]) evidence of infection with Borrelia hermsii. Sera also were tested for antibody to Borrelia burgdorferi. We identified 133 confirmed and 49 probable cases of TBRF. A jarisch-Herxheimer reaction was reported in 33 (54.1%) of 61 cases for which this information was available. Most patients who had antibodies to B. hermsii were serologically positive for B. burgdorferi, and WE demonstrated false positivity of testing for B. burgdorferi Thirty-five(21%) of 166 cases were unreported to public health authorities. In 52 cases, there were more than two relapses before the diagnosis. This study demonstrates that TBRF is underrecognized and underreported and map be falsely identified as Lyme disease.