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.

Rickettsial Infections among the Undifferentiated Febrile Patients Attending a Tertiary Care Teaching Hospital of Northern India: A Longitudinal Study.

BACKGROUND: Acute undifferentiated febrile illness (AUFI) is one of the most daunting challenges a physician faces in such settings. Among AUFI, rickettsial infections are most common and related infections (such as anaplasmosis, ehrlichiosis, and Q fever) which are caused by an unusual type of bacteria that can live only inside the cells of another organism. The present study was therefore planned with an objective to estimate the prevalence of rickettsial infection among patients of undifferentiated fever and to determine any association of socio-demographic characteristics with rickettsial disease. MATERIALS AND METHODS: Patients presenting with febrile illness and admitted or attending out-patient department of Sher-i-Kashmir Institute of Medical Sciences, Srinagar was approached and recruited in the study. Weil Felix Assay, enzyme-linked immunosorbent assay and indirect immunofluorescence assay were done to detect the anti-rickettsial antibodies. Serological evidence of a fourfold increase in IgG-specific antibody titer reactive with spotted fever group rickettsial antigen by indirect immunofluorescence antibody assays between paired serum specimens was considered a confirmatory diagnosis for the rickettsial disease. RESULTS: Most of the patients were males 61.6%, and most 46.2% were in the age group of 20 -39 years. Most of the patients, 80.8% belonged to rural areas, and 48% belonged to the upper middle (II) class of the socio-economic class according to modified Kuppuswamy scale. Of the studied participants, a majority, 47.0%, were determined undiagnosed, while 15.4% studied participants were diagnosed to have a rickettsial disease. In patients positive for typhus group, 67.8% were IgM positive, 28.5% were IgG positive, and only 3% were positive for IgM and IgG. In patients positive for Scrub Typhus Group, 32.7% were positive for IgM, and 62.0% were positive for IgG, and only 5.0% were positive for both IgM and IgG. In patients positive for spotted fever group, 36.1% were positive for IgM, and 58.5% were positive for IgG, and only 5.5% were positive for both IgM and IgG. The prevalence of rickettsial disease was found to be 11.3%. CONCLUSION: Rickettsial diseases, typhoid and brucellosis, were the most prevalent diseased diagnosed among patients reporting to hospitals with undifferentiated febrile illness. Clinicians must consider rickettsial diseases as one of the differential diagnosis while treating patients with fever.