Comparison of IgM capture ELISA with a commercial rapid immunochromatographic card test & IgM microwell ELISA for the detection of antibodies to dengue viruses

Background & objectives: There is a need for a reliable test for the early diagnosis of dengue fever (DF), which is now active in many parts of India especially in the post monsoon months. This study evaluated two commercial tests with an assay available from a national laboratory in India to obtain information and to make a comparison among the three tests as to which will be the most suited for the detection of IgM antibodies to dengue virus. Methods: An IgM capture ELISA (National Institute of Virology, Pune, India) was compared with two commercial tests, the PanBio Rapid Immunochromatographic Card Test (Brisbane, Australia) and the PanBio Microwell IgM ELISA for the detection of IgM antibodies to dengue virus. We tested 154 samples from individuals with febrile illnesses having DF - like symptoms. Results: The NIV IgM capture ELISA (MAC-ELISA) showed a high positivity rate (38.9%) as compared to the PanBio Rapid (22.7%) and the PanBio IgM ELISA (20.7%). The true prevalence of disease, sensitivity and specificity of the three tests were estimated using 2LC latent class models using expectation-maximization (EM) algorithm. The NIV MAC-ELISA showed a high sensitivity (96%) as compared to PanBio Rapid (73%) and PanBio IgM ELISA (72%). A subset of 68 samples (of the 154 tested) were analyzed by the NIV MAC-ELISA for IgM antibodies additionally to Japanese encephalitis (JE) and West Nile (WN) of which 31 samples showed positivity to either one, two or all three flaviviruses. Out of the 8 samples which were positive for dengue IgM alone by the NIV MAC-ELISA, only 2 (25%) each were picked up by the other 2 tests. While out of 7 samples positive for IgM to all three flaviviruses IgM by the NIV MAC-ELISA, 5 (71%) were picked up by the other 2 tests. Of the 5 that were picked up by the PanBio tests, 3 had the highest absorbance values to WN by the NIV MAC-ELISA, indicating cross reactivity by PanBio tests. Interpretation & conclusion: The MAC-ELISA though a 3 day procedure, would be a valuable screening test for the detection of IgM to dengue in routine diagnostic laboratories because of its high sensitivity and specificity rates. The test uses specific viral antigens to detect IgM antibodies not only to dengue but also to JE and West Nile as a result of which IgM antibodies to all the 3 commonly encountered flaviviruses can be detected in a single run. It also has the advantage in that depending on the strength of the antibody units obtained to a specific flaviviral antigen, presumptive diagnosis as to which particular arboviral infection has occurred can be made in conjuction with clinical presentation.