Comparison between indirect fluorescent antibody and Weil-Felix tests for detecting antibodies against rickettsia.

Comparative evaluation of indirect fluorescent antibody test (IFAT) and Weil-Felix test (WFT) was carried out for detecting rickettsial antibodies in 102 patients with pyrexia of unknown origin (P.U.O.), 20 brucellosis cases and 20 normal healthy controls (N.H.C.). Of 102 sera of cases with P.U.O., antibodies against rickettsia could be detected in 11 (10.7 per cent) cases by IFAT and in 10 (9.8 per cent) cases by WFT, but amongst these 10 sera, antibodies could be detected only in six by IFAT. All 20 brucella positive sera were negative for rickettsia by IFAT but by WFT in 6 sera antibodies against rickettsia could be detected and 20 N.H.C. sera were negative by both the tests. Thus the advantages of IFAT over WFT in detecting antibodies against rickettsia in terms of sensitivity and specificity make it a more reliable test.