Laboratory diagnosis of Rocky Mountain spotted fever.

To examine the use of the laboratory in the diagnosis of Rocky Mountain spotted fever and to determine the specificity and sensitivity of the Weil-Felix test, hemagglutination, complement fixation, and skin biopsy immunofluorescence in the hospital, we reviewed our experience during th year 1978. Sera were submitted from 142 patients and skin biopsies from 16 patients suspected of having RMSF. Sensitivity rates of methods in the acute phase were skin biopsy, 70%; Proteus OX-19 agglutination, 65%; hemagglutination, 19%; Proteus OX-2 agglutination, 18%; and CF, 0%. Overall specificity rates were skin biopsy, 100%; hemagglutination, 99%; and agglutination of Proteus OX-2 96% and OX-19 78%. Major problems were failure to submit convalescent serum and nonspecificity of Weil-Felix titer of 1:160. Two cases illustrate the importance of skin biopsy and serologic results. Immunofluorescent examination of skin biopsies for Rickettsia rickettsii is the best procedure currently available for early diagnosis.