Meagan F. Vaughn et al, September 2014, doi:10.1128/JCM.01733-14
Increasing entomologic and epidemiologic evidence suggests that spotted fever group rickettsiae (SFGR) other than Rickettsia rickettsii are responsible for spotted fever rickettsioses in the US. A retrospective seroepidemiologic study was conducted on stored acute and convalescent sera that had been submitted for Rocky Mountain spotted fever testing to the North Carolina State Laboratory of Public Health. We evaluated the serologic reactivity of the paired sera to R. rickettsii, R. parkeri, and R. amblyommii antigens.
Of the 106 eligible pairs tested, 21 patients seroconverted to one or more antigens. Cross-reactivity to multiple antigens was observed in ten patients and seroconversions to single antigens occurred in 11 patients, including one againstR. rickettsii, four against R. parkeri, and six against R. amblyommii. Cross-absorption of cross-reactive sera and/or western blots identified two presumptive cases of infection with R. parkeri, two presumptive cases of infection with R. rickettsii, and one presumptive case of infection with R. amblyommii. These findings suggest that species of SFGR other than R. rickettsii are associated with illness among North Carolina residents and that serologic testing using R. rickettsiiantigen may miss cases of spotted fever rickettsioses caused by other species of SFGR.