infectious diseases
Rocky Mountain Spotted Fever (RMSF)
Diagnosis of RMSF
History and physical examination Biopsy of rash with fluorescent antibody staining to detect organisms Acute and convalescent serologic testing (serologic testing not useful acutely) Polymerase chain reaction (PCR) Clinicians should suspect Rocky Mountain spotted fever in any seriously ill patient who lives in or near a wooded area anywhere in the Western Hemisphere and has unexplained fever, headache, and prostration, with or without a history of tick contact. A history of tick bite is elicited in about 60% of patients (seeCDC: RMSF). Testing is usually required to confirm RMSF but because of the limitations of currently available tests, clinicians typically must make treatment decisions before receiving results of confirmatory testing. If patients have a rash, a skin biopsy should be taken from the rash site. PCR or immunohistochemical staining, which can provide fairly rapid results, is used. However, a negative test result does not justify withholding treatment when clinical manifestations suggest RMSF. Culture ofR. rickettsiiis available only at specialized laboratories. Negative test results for RMSF do not justify withholding treatment when clinical manifestations suggest RMSF. Serologic tests are not useful for acute diagnosis because they usually become positive only during convalescence. Indirect immunofluorescence assay using 2 paired samples is usually done. For details, see Diagnosis . 