EVALUATION OF IGM ELISA, WEIL FELIX TEST AND INDIRECT IMMUNOFLUORESCENCE ASSAY IN THE DIAGNOSIS OF SCRUB TYPHUS.

Dr Pooja Raghunath, Dr P. Jose Paul, Dr Seema Oommen, Dr Sreeja Nair, Dr Archana Sasimohan

Abstract


Scrub typhus is an acute febrile illness caused by Orientia tsutsugamushi. There are reports of resurgence of scrub typhus
in different parts of India including Kerala. Many cases go undiagnosed due to the lack of knowledge regarding the
diagnostic test to be used. This study was undertaken at Pushpagiri Institute of Medical Sciences and Research Centre, Tiruvalla in the
Department of Microbiology from January 2014 to September 2015, to assess the validity of various tests in diagnosing scrub typhus. A total of 94
samples were subjected to IgM ELISA, Weil Felix (WF) test and Indirect Immunouorescence assay(IFA). The agreement between ELISA, IFA
and Weil Felix test was assessed by κ (kappa) coefcient of Cohen using SPSS version 17. The sensitivity and specicity of ELISA with respect to
IFA was 100% and 94.67% respectively, and that of IFA with respect to ELISA was 82.61% and 100% respectively. The sensitivity and
specicity of WF test with respect to ELISA was 43.48 and 100% respectively and that of WF test with respect to IFA was 52.63% and 100%
respectively. Although IgM ELISA is highly sensitive, it cannot be relied upon as the sole diagnostic test due to high false positivity. WF test is not
a sensitive test, but when positive it is rather specic. IFA has high sensitivity and specicity, but is unsuitable for moderately equipped
laboratories. Hence, we suggest that scrub typhus could be diagnosed using a combination of IgM ELISA and WF test and these tests should be
included in the panel of serological tests ordered for patients presenting with undifferentiated febrile illnesses.


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