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
Probable: 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)
Confirmed: a clinically compatible case that is laboratory
confirmed