Fig. 1

Laboratory diagnoses of SFGR, TGR and URI cases, Ontario, Canada (2013–2018)^a. Abbreviations: +, immunofluorescent assay (IFA) IgG titer ≥1:64 (seropositive); −, IFA IgG titer < 1:64 (seronegative); PRI, previous rickettsial infection; SFGR, spotted fever group rickettsiae; TGR, typhus group rickettsiae; URI, unspecified Rickettsia infection. ^a We base this decision tree on serology and clinical signs and symptoms. Confirmed cases: 4-fold increase in IgG titers in paired acute and convalescent sera, with evidence of fever plus one other sign or symptom. Possible cases: IgG ≥ 1:64, with evidence of fever and one other sign or symptom. PRI cases: IgG ≥ 1:64, without evidence of fever and one other sign or symptom