Comparative evaluation of serological tests used for the diagnosis of rickettsial diseases prevalent in the temperate region of North India.

PURPOSE: The clinical manifestations of rickettsial diseases mimic other endemic infections with similar presentations thus posing a serious challenge to clinicians for their diagnosis. For the diagnosis of rickettsial disease serological tests like Weil Felix, ELISA and IFA are used. There are limited studies that have evaluated different serological tests for the diagnosis of rickettsial diseases. Therefore, the present study was undertaken to evaluate the ELISA and Weil Felix test for the diagnosis of rickettsial diseases prevalent in this region.

METHODS

Samples from 281 patients clinically suspected of rickettsial diseases were tested for spotted fever group (SFG), typhus group (TG) and scrub typhus group (STG) by Weil Felix, ELISA and IFA was taken as the gold standard. Baseline titers and cut-off ODs were calculated by taking samples from healthy blood donors.

RESULTS

The sensitivity, specificity, positive and negative predictive value of Weil Felix test ranged from 30% to 44%, 83.46%-97.86%, 9%-77%, 92-96% respectively. The sensitivity and specificity, positive and negative predictive value of ELISA ranged from 80.77% to 96.15%, 96.33%-98.43%, 70.21%-88.64%, 92.89%-99.60% respectively. Maximum cross-reactions were observed between SFG and STG by the Weil Felix test and between STG and TG by ELISA.

CONCLUSIONS

ELISA was found to be sensitive and specific for the diagnosis of rickettsial diseases. It is easy to perform, does not require a technical expert for result interpretation and a large number of samples can be processed at a time.