The Expanding Spectrum of Eschar-Associated Rickettsioses in the United States

Background: Until recently, Rickettsia rickettsii was the only substantiated cause of tick-borne spotted fever group (SFG) rickettsiosis in humans in the United States. Rickettsia parkeri, originally thought to be nonpathogenic in humans, was recently proved to be another cause of tick-borne SFG rickettsiosis. Observations: We report 3 cases of SFG rickettsiosis and discuss the epidemiology, clinical presentation, histopathologic features, and laboratory findings that support confirmed or probable diagnoses of R parkeri infection and describe the expanding list of eschar-associated SFC rickettsioses recognized in US patients. Conclusions: The SFG rickettsioses share many clinical manifestations and extensive antigenic cross-reactivity that may hamper specific confirmation of the causative agent.