Neutralizing antibody responses to SARS-CoV-2 in COVID-19 patients.

BACKGROUND & OBJECTIVES: The global pandemic caused by SARS-CoV-2 virus has challenged public health system worldwide due to the unavailability of approved preventive and therapeutic options. Identification of neutralizing antibodies (NAb) and understanding their role is important. However, the data on kinetics of NAb response among COVID-19 patients are unclear. To understand the NAb response in COVID-19 patients, we compared the findings of microneutralization test (MNT) and plaque reduction neutralization test (PRNT) for the SARS-CoV-2. Further, the kinetics of NAb response among COVID-19 patients was assessed. METHODS: A total of 343 blood samples (89 positive, 58 negative for SARS-CoV-2 and 17 cross-reactive and 179 serum from healthy individuals) were collected and tested by MNT and PRNT. SARS-CoV-2 virus was prepared by propagating the virus in Vero CCL-81 cells. The intra-class correlation was calculated to assess the correlation between MNT and PRNT. The neutralizing endpoint as the reduction in the number of plaque count by 90 per cent (PRNT90) was also calculated. RESULTS: The analysis of MNT and PRNT quantitative results indicated that the intra-class correlation was 0.520. Of the 89 confirmed COVID-19 patients, 64 (71.9%) showed NAb response. INTERPRETATION & CONCLUSIONS: The results of MNT and PRNT were specific with no cross-reactivity. In the early stages of infection, the NAb response was observed with variable antibody kinetics. The neutralization assays can be used for titration of NAb in recovered/vaccinated or infected COVID-19 patients.

Development of indigenous IgG ELISA for the detection of anti-SARS-CoV-2 IgG.

BACKGROUND & OBJECTIVES: Since the beginning of the year 2020, the pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) impacted humankind adversely in almost all spheres of life. The virus belongs to the genus Betacoronavirus of the family Coronaviridae. SARS-CoV-2 causes the disease known as coronavirus disease 2019 (COVID-19) with mild-to-severe respiratory illness. The currently available diagnostic tools for the diagnosis of COVID-19 are mainly based on molecular assays. Real-time reverse transcription-polymerase chain reaction is the only diagnostic method currently recommended by the World Health Organization for COVID-19. With the rapid spread of SARS-CoV-2, it is necessary to utilize other tests, which would determine the burden of the disease as well as the spread of the outbreak. Considering the need for the development of such a screening test, an attempt was made to develop and evaluate an IgG-based ELISA for COVID-19. METHODS: A total of 513 blood samples (131 positive, 382 negative for SARS-CoV-2) were collected and tested by microneutralization test (MNT). Antigen stock of SARS-CoV-2 was prepared by propagating the virus in Vero CCL-81 cells. An IgG capture ELISA was developed for serological detection of anti-SARS-CoV-2 IgG in serum samples. The end point cut-off values were determined by using receiver operating characteristic (ROC) curve. Inter-assay variability was determined. RESULTS: The developed ELISA was found to be 92.37 per cent sensitive, 97.9 per cent specific, robust and reproducible. The positive and negative predictive values were 94.44 and 98.14 per cent, respectively. INTERPRETATION & CONCLUSIONS: This indigenously developed IgG ELISA was found to be sensitive and specific for the detection of anti-SARS-CoV-2 IgG in human serum samples. This assay may be used for determining seroprevalence of SARS-CoV-2 in a population exposed to the virus.

Direct Saliva Real-time Polymerase Chain Reaction Assay Shows Low Birth Prevalence of Congenital Cytomegalovirus Infection in Urban Western India.

BACKGROUND: Congenital cytomegalovirus (cCMV) infection is the leading infectious cause of mental retardation, developmental delay and sensorineural deafness. Nonprimary infection plays a major role in transmission of this infection in countries with high maternal seroprevalence. Noninvasive sampling and testing is a useful alternative to traditional methods of laboratory detection of congenital CMV infection. The present study was conducted to understand birth prevalence of cCMV infection using molecular techniques, in an urban setting of a developing country with evidence of high maternal seroprevalence. METHODS: Universal newborn screening for cCMV was performed for 750 infants born at a tertiary care center in Western India. Real-time polymerase chain reaction was directly carried out on saliva samples. Follow-up laboratory testing of saliva, urine and blood was performed for neonates identified as positive. Sequential clinical follow-up was offered to the affected infants. RESULTS: A birth prevalence of 0.4% (95% CI: 0.13-1.2) was observed with 3 of 750 babies confirmed to be positive for cCMV infection. All 3 babies were born to seropositive mothers (anti-CMV immunoglobulin G positive). One of the babies detected was symptomatic with sepsis like features. All of them survived and did not develop any sequelae up to 1 year of age. CONCLUSION: The use of direct real-time polymerase chain reaction of saliva samples can be considered as a feasible option for newborn screening of congenital CMV infection in developing countries. Relatively low birth prevalence of cCMV infection was observed in our study, which needs to be corroborated through further studies.