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 conjunction with clinical presentation.

SSPE - The continuing challenge: A study based on serological evidence from a teritary care centre in India.

PURPOSE: To assess the prevalence of subacute sclerosing panencephalitis (SSPE). METHODS: In the period June 96 to December' 98 an analysis for measles virus (MV) antibody was carried out on 103 serum-CSF pairs received from patients clinically suspected of SSPE. Measles antibody was detected in an indirect immunofluorescent assay (IIF) test. RESULTS: Antibody to measles was detectable in 49 (48%) of the serum-CSF pairs tested, a diagnostic criterion for SSPE. Antibody titers ranged from 20 to 1280 in serum and neat to 32 in CSF. The serum: CSF ratio ranged from 5:1 to 80:1. Of the 49 patients diagnosed to have SSPE, 36 were males and 13 females, and the age of the patients at the time of diagnosis of SSPE ranged from 5 to 26 years. Ten of the SSPE patients gave a history of measles vaccination. CONCLUSIONS: Inadequate vaccine coverage and quality of vaccine used continue to have an impact on occurrence of SSPE.

Characterization of antibody response to human cytomegalovirus in Indian renal transplant patients.

BACKGROUND & OBJECTIVES: Cytomegalovirus (CMV) disease in seroendemic transplant populations is due to reactivation of the virus, or reinfection. In this context, the antibody response is likely to influence presentation, clinical severity and outcome of the disease, and may provide a diagnostic and prognostic marker. This study was carried out in Indian renal transplant patients and healthy adults to characterize the antibody response to cytomegalovirus. METHODS: Thirty three transplant recipients with CMV illness (symptomatology with IgM and/or nPCR positive status), 20 recipients who were asymptomatic in the 6 months of follow up after transplantation and 62 healthy controls were investigated for markers of CMV infection. These individuals were tested for IgG avidity and neutralizing antibody by ELISA techniques. RESULTS: All 53 transplant recipients were found to have an IgG avidity index of > 50 per cent. Antibody to a CMV envelope glycoprotein gB/AD-1 (putative neutralizing antibody) was expressed as S/N ratio and was > or = 5 in asymptomatic (65%) and symptomatic (27%) immunosuppressed renal transplant recipients. However, none of the 53 CMV IgG positive healthy controls were positive for neutralizing antibodies S/N ratio > or = 5 (S/N ratio = sample mean OD/mean OD of 3 negative controls in each run). We observed the simultaneous presence of CMV PCR signal in leukocytes and neutralizing antibody (S/N ratio > or = 5) in the plasma in 22 (41.5%) of the 53 renal transplant recipients. INTERPRETATION & CONCLUSIONS: In this study among the immunosuppressed transplant patients we observed an association between symptomatic disease and the relative absence of neutralizing antibodies. The neutralizing antibodies are less frequently demonstrable among controls; while appearance in a higher proportion of asymptomatic recipients especially in association with high IgG avidity (> 90%) is suggestive of its role in control of CMV disease despite reactivation as evidenced by DNAemia while on immunosuppressive therapy.

E test as an alternative to conventional MIC determination for surveillance of drug resistant Streptococcus pneumoniae.

A commercial E test was compared with the standard agar dilution method for the determination of minimum inhibitory concentration (MIC) of penicillin, erythromycin, chloramphenicol and cefotaxime for 36 strains of Streptococcus pneumoniae from patients with invasive diseases. Additional strains were tested for MIC values for penicillin (6), erythromycin (14) and cefotaxime (13) for a better statistical evaluation. Besides, 5 reference standards with predetermined MIC values obtained from WHO pneumococcal reference center at Copenhagen, Denmark were tested for penicillin and erythromycin, for quality assessment using both agar dilution as well as E test methods. An overall agreement within +/- 2 dilutions was noted for 97 per cent of the strains tested for all the antimicrobials. A high degree of correlation was noted for erythromycin (r = 1), penicillin (r = 0.99), chloramphenicol (r = 0.95) and cefotaxime (r = 0.9). In MIC determination of a single antimicrobial for diagnostic purpose, E test was found to be more cost effective than conventional agar dilution method. E test was simple to perform, easy to interpret and a valid method for MIC determination of antimicrobials for S. pneumoniae in our center.