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Microbiol Spectr ; 9(3): e0056021, 2021 12 22.
Article in English | MEDLINE | ID: covidwho-1546467


Serological tests are beneficial for recognizing the immune response against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). To identify protective immunity, optimization of the chemiluminescent reduction neutralizing test (CRNT) is critical. Whether commercial antibody tests have comparable accuracy is unknown. Serum samples were obtained from COVID-19 patients (n = 74), SARS-CoV-2 PCR-negative (n = 179), and suspected healthy individuals (n = 229) before SARS-CoV-2 variants had been detected locally. The convalescent phase was defined as the period after day 10 from disease onset or the episode of close contact. The CRNT using pseudotyped viruses displaying the wild-type (WT) spike protein and a commercial anti-receptor-binding domain (RBD) antibody test were assayed. Serology for the B.1.1.7 and B.1.351 variants was also assayed. Both tests concurred for symptomatic COVID-19 patients in the convalescent phase. They clearly differentiated between patients and suspected healthy individuals (sensitivity: 95.8% and 100%, respectively; specificity: 99.1% and 100%, respectively). Anti-RBD antibody test results correlated with neutralizing titers (r = 0.31, 95% confidence interval [CI] 0.22-0.38). Compared with the WT, lower CRNT values were observed for the variants. Of the samples with ≥100 U/mL by the anti-RBD antibody test, 77.8% and 88.9% showed ≥50% neutralization against the B.1.1.7 and the B.1.351 variants, respectively. Exceeding 100 U/mL in the anti-RBD antibody test was associated with neutralization of variants (P < 0.01). The CRNT and commercial anti-RBD antibody test effectively classified convalescent COVID-19 patients. Strong positive results with the anti-RBD antibody test can reflect neutralizing activity against emerging variants. IMPORTANCE This study provides a diagnostic evidence of test validity, which can lead to vaccine efficacy and proof of recovery after COVID-19. It is not easy to know neutralization against SARS-CoV-2 in the clinical laboratory because of technical and biohazard issues. The correlation of the quantitative anti-receptor-binding domain antibody test, which is widely available, with neutralizing test indicates that we can know indirectly the state of acquisition of functional immunity against wild and variant-type viruses in the clinical laboratory.

Antibodies, Viral/blood , COVID-19 Serological Testing/methods , COVID-19/diagnosis , COVID-19/immunology , Neutralization Tests/methods , Protein Binding/immunology , SARS-CoV-2/immunology , Adult , Aged , Antibodies, Neutralizing/immunology , Female , Humans , Male , Middle Aged , SARS-CoV-2/classification , Vaccine Efficacy , Viral Pseudotyping , Young Adult
J Infect Chemother ; 28(2): 347-351, 2022 Feb.
Article in English | MEDLINE | ID: covidwho-1510011


Genetic testing using reverse transcriptase real-time polymerase chain reaction (rRT-PCR) is the mainstay of diagnosis of COVID-19. However, it has not been fully investigated whether infectious viruses are contained in SARS-CoV-2 genome-positive specimens examined using the rRT-PCR test. In this study, we examined the correlation between the threshold Cycle (Ct) value obtained from the rRT-PCR test and virus isolation in cultured cells, using 533 consecutive clinical specimens of COVID-19 patients. The virus was isolated from specimens with a Ct value of less than 30 cycles, and the lower the Ct value, the more efficient the isolation rate. A cytopathic effect due to herpes simplex virus type 1 contamination was observed in one sample with a Ct value of 35 cycles. In a comparison of VeroE6/TMPRSS2 cells and VeroE6 cells used for virus isolation, VeroE6/TMPRSS2 cells isolated the virus 1.7 times more efficiently than VeroE6 cells. There was no significant difference between the two cells in the mean Ct value of the detectable sample. In conclusion, Lower Ct values in the PCR test were associated with higher virus isolation rates, and VeroE6/TMPRSS2 cells were able to isolate viruses more efficiently than VeroE6 cells.

COVID-19 , SARS-CoV-2 , Cell Line , Diagnostic Tests, Routine , Humans , Real-Time Polymerase Chain Reaction