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NOTE: A surveillance case definition is a set of uniform criteria used to define a disease for public health surveillance. Surveillance case definitions enable public health officials to classify and count cases consistently across reporting jurisdictions. Surveillance case definitions are not intended to be used by healthcare providers for making a clinical diagnosis or determining how to meet an individual patient’s health needs.

Clinical Description

A tickborne febrile illness most commonly characterized by acute onset and 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 Rickettsia rickettsii antigen by immunofluorescence antibody (IFA), complement fixation (CF), latex agglutination (LA), microagglutination (MA), or indirect hemagglutination antibody (IHA) test in acute- and convalescent-phase specimens ideally taken greater than or equal to 3 weeks apart, OR
  • Positive polymerase chain reaction assay to R. rickettsii, OR
  • Demonstration of positive immunofluorescence of skin lesion (biopsy) or organ tissue (autopsy), OR
  • Isolation of R. rickettsii from clinical specimen

Case Classification


A clinically compatible case with a single IFA serologic titer of greater than or equal to 64 or a single CF titer of greater than or equal to 16 or other 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 an LA, IHA, or MA test)


A clinically compatible case that is laboratory confirmed

Related Case Definition(s)