Laboratory diagnosis of Mediterranean spotted fever by immunofluorescent demonstration of Rickettsia conorii in cutaneous lesions.

Indirect immunofluorescent staining was performed on cryostat sections of skin biopsy specimens from 21 patients. In six of the 11 cases finally diagnosed as Mediterranean spotted fever, coccobacillary forms of Rickettsia conorii were identified in these sections. A factor recognized as contributing to false-negative results was prior treatment with tetracycline. No false-positive results were obtained for 10 patients whose final diagnosis was not Mediterranean spotted fever. This laboratory test can aid in the early diagnosis of severe and atypical forms of Mediterranean spotted fever.