EVALUATION OF SPECIFICITY OF INDIRECT ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR DIAGNOSIS OF HUMAN Q-FEVER

Ninety-five acute- and convalescent-phase serum specimens from 48 pati ents suspected of having rickettsial or Legionella infections were ass ayed for antibodies to Coxiella burnetii, the causative agent of Q fev er. To evaluate the specificity of the indirect enzyme-linked immunoso rbent assay (ELISA) for human Q fever, we compared the ELISA results w ith those of the indirect immunofluorescence antibody (IFA) test. The ELISA data were analyzed by two different criteria for a positive test . The first criterion for positive results by ELISA was based upon dia gnostic titers established in a study of 150 subjects who had no demon strable cellular or humoral immune responses to C. burnetii phase I or phase II whole cells or phase I lipopolysaccharide. The second criter ion was based upon diagnostic antibody titers in a study of 51 subject s who had been diagnosed as having clinical Q fever and had fourfold o r greater rises in humoral immune responses to C. burnetii phase I and phase II whole-cell antigens. A comparison of the ELISA and IFA test results of the 95 serum specimens indicated excellent agreement betwee n the tests (Kappa = 92.9%; P < 0.05). None of the 38 patients whose e tiologies were confirmed serologically as Legionnaires' disease or ric kettsial diseases other than Q fever were classified as positive for C . burnetii by the ELISA. Only one patient identified by the IFA test a s having Q fever was not scored positive by the ELISA. These results s uggest that the ELISA is useful for epidemiologic screening and as a d iagnostic test for human Q fever.