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Rocky Mountain Spotted Fever (RMSF) (Rickettsia rickettsii)
1990 Case Definition

Clinical Description

An illness most commonly characterized by acute onset and fever, usually accompanied by myalgia, headache, and petechial rash (on the palms and soles in two-thirds of the cases)

Laboratory Criteria for Diagnosis

  • Fourfold or greater rise in antibody titer to the spotted fever group antigen by immunofluorescent antibody (IFA), complement fixation (CF), latex agglutination (LA), microagglutination (MA), or indirect hemagglutination (IHA) test, or a single titer greater than or equal to 64 by IFA or greater than or equal to 16 by CF
  • Demonstration of positive immunofluorescence of skin lesion (biopsy) or organ tissue (autopsy)
  • Isolation of Rickettsia rickettsii from clinical specimen

Case Classification


A clinically compatible case with supportive serology (fourfold rise in titer or a single titer greater than or equal to 320 by Proteus OX-19 or OX-2, or a single titer greater than or equal to 128 by LA, IHA, or MA test)


A case that is laboratory confirmed