Determination of Cutoff of IgM ELISA for Diagnosis of Scrub typhus in Hilly Northern State of Himachal Pradesh

Abstract:

The aim of the study was to determine geographically relevant cutoffs for IgM ELISA in Himachal Pradesh. A total of 392 individuals including 292 patients of all age groups with clinically suspected scrub typhus and 100 healthy people were enrolled after taking a proper consent at Indira Gandhi Medical College, Shimla. An indirect ELISA that detects IgM antibodies to Orientia tsutsugamushi was performed in all serum samples. The serum samples from patients were subjected to IgM immunofluorescent antibody (IFA) (Fuller Laboratories, USA). A receiver operating characteristic (ROC) curve was drawn for ELISA to generate cutoff for the test. A total of 192 patients were found to be positive for scrub typhus. A set of 100 sera samples collected from healthy volunteers from Shimla were used to establish region specific cutoff for IgM ELISA. The cut off calculated from healthy volunteer was mean OD +3 standard deviation = 0.5. The ROC curve analysis of 392 participants revealed a cutoff-OD value of 0.46 with sensitivity and specificity of 91.7% and 99.5% respectively. Hence, a cutoff-OD value of 0.46 or 0.5 can be used as the cutoff for the diagnosis of scrub typhus for Himachal Pradesh based on our findings.

Keywords:

Geographically relevant cutoffs, indirect ELISA, IgM antibodies, receiver operating characteristic (ROC) curve.

Citation:

Gupta, A., 2018. Determination of Cutoff of IgM ELISA for Diagnosis of Scrub typhus in Hilly Northern State of Himachal Pradesh. PSM Microbiol. 3(1): 1-3.

Full Text

INTRODUCTION

Scrub typhus is an acute febrile illness caused by an obligate intra-cellular gram negative bacterium, Orientia tsutsugamushi. It is transmitted to humans by the bite of chiggers. It is a public health problem in Asia, where about 1 million new cases are identified annually and 1 billion people may be at risk for this disease. Mortality occurs in 30% to 50% of untreated cases (Diprabhanu et al, 2007). Diagnostic techniques like IgM ELISA and IgM IFA help in early diagnosis and treatment. Though, IFA is the serological gold standard (Manuj et al, 2015) , IgM ELISA have remained the mainstay of diagnosis in various laboratories as it provides an objective result and has sensitivity similar to IFA (McDade JE, 1998). A four-fold rise in serum antibody is desired for diagnosis (Gavin et al, 2010). However, for guidance of initial treatment, there is a need for rapid diagnosis at the time of admission. One of the biggest challenges in the diagnosis of scrub typhus in this region is the unavailability of a standardized cutoff for these serological tests. The study was conducted to determine geographically relevant cutoffs for IgM ELISA in Himachal Pradesh.

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