Clinical assessment of SARS-CoV-2 infectivity by rapid antigen test compared with virus isolation.

Although real-time reverse transcriptase polymerase chain reaction (real-time RT-PCR) remains as a golden standard for detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, it can not be easily expanded to large-scaled screening during outbreaks, and the positive results do not necessarily correlate with infectious status of the identified subjects. In this study, the performance of Vstrip® RV2 COVID-19 Antigen Rapid Test (RAT) and its correlation with virus infectivity was examined by virus culture using 163 sequential respiratory specimens collected from 26 SARS-CoV-2 infected patients. When the presence of cytopathic effects (CPE) in cell culture was used as a reference method for virus infectivity, the sensitivity, specificity and accuracy of Vstrip® RV2 COVID-19 Antigen Rapid Test was 96.43%, 89.63%, and 90.8%, respectively. The highest Ct value was 27.7 for RdRp gene and 25.79 for E gene within CPE-positive samples, and the highest Ct value was 31.9 for RdRp gene and 29.1 for E gene within RAT positive samples. When the Ct values of specimens were below 25, the CPE and RAT results had high degree of consistency. We concluded that the RAT could be a great alternative method for determining the infectious potential of individuals with high viral load.

Evolution of neutralizing antibodies and cross-activity against different variants of SARS-CoV-2 in patients recovering from COVID-19.

BACKGROUND: Patients recovering from COVID-19 may need vaccination against SARS-CoV-2 because acquired immunity from primary infection may wane, given the emergence of new SARS-CoV-2 variants. Understanding the trends of anti-spike IgG and neutralizing antibody titers in patients recovering from COVID-19 may inform the decision made on the appropriate interval between recovery and vaccination. METHODS: Participants aged 20 years or older and diagnosed with COVID-19 between January and December, 2020 were enrolled. Serum specimens were collected every three months from 10 days to 12 months after the onset of symptom for determinations of anti-spike IgG and neutralizing antibody titers against SARS-CoV-2 Wuhan strain with D614G mutation, alpha, gamma and delta variants. RESULTS: Of 19 participants, we found a decreasing trend of geometric mean titers of anti-spike IgG from 560.9 to 217 and 92 BAU/mL after a 4-month and a 7-month follow-up, respectively. The anti-spike IgG titers declined more quickly in the ten participants with severe or critical disease than the nine participants with only mild to moderate disease between one month and seven months after SARS-CoV-2 infection (-8.49 vs - 2.34-fold, p < 0.001). The neutralizing activity of the convalescent serum specimens collected from participants recovering from wild-type SARS-CoV-2 infection against different variants was lower, especially against the delta variants (p < 0.01 for each variant with Wuhan strain as reference). CONCLUSION: Acquired immunity from primary infection with SARS-CoV-2 waned within 4-7 months in COVID-19 patients, and neutralizing cross-activities against different SARS-CoV-2 variants were lower compared with those against wild-type strain.

Virological, serological, and antiviral studies in an imported human case of avian influenza A(H7N9) virus in Taiwan.

We describe the clinical course and virological characteristics of the first H7N9 influenza case in a Taiwanese patient; this patient had detectable viruses in the airway for 2 weeks, during which time an oseltamivir resistance-associated R292K mutation rapidly emerged. Anti-H7N9 antibody was detected 21 days after onset of symptoms, when H7N9 viral load declined significantly.

Comparison of Abbott AxSYM and Roche Elecsys 2010 for measurement of BNP and NT-proBNP.

BACKGROUND: B-type natriuretic peptide (BNP) and N-terminal pro-brain natriuretic peptide (NT-proBNP) are small cardiac hormones released from the heart. They can be used as an important aid to diagnose congestive heart failure (CHF). METHODS: We compared the performances of the Abbott AxSYM and Roche Elecsys 2010 for the measurement of BNP and NT-proBNP. The first method uses a microparticle enzyme-linked immunoassay, whereas the other uses chemiluminescent immunometric assay. RESULTS: The CVs using pooled sera ranged from 3.7% to 12.7% for the AxSYM and 0.9% to 2.2% for the Elecsys 2010. The Passing and Bablok regression was Elecsys 2010 NT-proBNP=7.23xAxSYM BNP+2.53. The BNP in EDTA plasma was more stable than in serum. The immunoreactivity difference of NT-proBNP in serum or EDTA plasma was within 10% when stored at 4 degrees Celsius or 25 degrees Celsius for 72 h. Receiver operating characteristic (ROC) curves were different for both assays, and the areas under the curves were 0.704 and 0.841 for the AxSYM and Elecsys 2010 method, respectively. CONCLUSIONS: Both assays were not entirely specific for heart failure. The precision and stability for NT-proBNP was better than for BNP in serum. It is important to use method-appropriate reference ranges (or cutoff) for the BNP and NT-proBNP, respectively, in the assessment of CHF.