Positivization time of a COVID-19 rapid antigen self-test predicts SARS-CoV-2 viral load: a proof of concept.

OBJECTIVES: This proof of concept study was aimed to validate the hypothesis that the time of positivization of SARS-CoV-2 self-performed rapid diagnostic tests (RDTs) may reflect the actual viral load in the specimen. METHODS: A SARS-CoV-2 positive sample with high viral load was diluted and concomitantly assayed with molecular assay (Xpert Xpress SARS-CoV-2) and RDT (COVID-VIRO ALL IN RDT). The (mean cycle threshold; Ct) values and RDT positivization times of these dilutions were plotted and interpolated by calculating the best fit. The parameters of this equation were then used for converting the positivization times into RDT-estimated SARS-CoV-2 Ct values in routine patient samples. RESULTS: The best fit between measured and RDT-estimated Ct values could be achieved with a 2-degree polynomial curve. The RDT-estimated Ct values exhibited high correlation (r=0.996) and excellent Deming fit (y=1.01 × x - 0.18) with measured Ct values. In 30 consecutive patients with positive RDT test, the correlation between RDT positivization time and measured Ct value was r=0.522 (p=0.003). The correlation of RDT-estimated and measured Ct values slightly improved to 0.577 (Deming fit: y=0.44 × x + 11.08), displaying a negligible bias (1.0; 95% CI, -0.2 to 2.2; p=0.105). Concordance of RDT-estimated and measured Ct values at the <20 cut-off was 80%, with 0.84 sensitivity and 0.73 specificity. CONCLUSIONS: This proof of concept study demonstrates the potential feasibility of using RDTs for garnering information on viral load in patients with acute SARS-CoV-2 infection.

Assessment of humoral and cellular immunity after bivalent BNT162b2 vaccination and potential association with reactogenicity.

OBJECTIVES: This study investigated the feasibility and clinical value of using a novel, automated and high-throughput SARS-CoV-2 Interferon Gamma Release Assay (IGRA), combined with total anti-SARS-CoV-2 antibodies assessment, for evaluating the immune response after bivalent BNT162b2 vaccination. METHODS: A cohort of healthcare workers, who already underwent primary vaccination and boosting with monovalent BNT162b2 vaccine, received a booster dose of the new BNT162b2 bivalent formulation. Blood samples were taken immediately before vaccination (T0) and 1 month afterwards (T1). Humoral and cellular immunity were assayed with Roche Elecsys Anti-SARS-CoV-2 and Roche Elecsys IGRA SARS-CoV-2, respectively. RESULTS: The study population consisted of 51 subjects (median age: 43 years; 51% females). Total anti-SARS-CoV-2 antibodies and IGRA SARS-CoV-2 values increased at T1 from 9,050 to 25,000 BAU/mL (p<0.001), and from 0.44 to 0.78 IU/mL (p=0.385), accounting for median increase of 2.0 and 1.6 folds, respectively. Increased T1 values of total anti-SARS-CoV-2 antibodies and IGRA SARS-CoV-2 were recorded in 100% and 68.6% subjects, respectively. In those with baseline values below the median, post-vaccine levels displayed larger increases of 3.3 and 5.1 folds for anti-SARS-CoV-2 total antibodies and IGRA SARS-CoV-2, respectively. The variation of total anti-SARS-CoV-2 antibodies was inversely associated with their T0 values (r=-0.97; p<0.001), whilst that of IGRA SARS-CoV-2 was inversely associated with its T0 value (r=-0.58; p<0.001). No other signifcant associations were found with demographical or clinical variables, including side effects. CONCLUSIONS: The bivalent BNT162b2 vaccine booster enhances humoral and cellular immunity against SARS-CoV-2, especially in recipients with lower baseline biological protection.

Real-world assessment of the clinical performance of COVID-VIRO ALL IN rapid SARS-CoV-2 antigen test.

OBJECTIVES: Since the external validation of severe acute respiratory syndrome coronavirus 2 antigen rapid diagnostic tests (SARS-CoV-2 RDT-Ags) is a necessary requisite before they can be introduced into routine clinical practice, this study reports the results of a real-world assessment of the clinical performance of the new COVID-VIRO ALL IN device. METHODS: The study population consisted in 165 outpatients (median age: 43 years, range: 14-68 years; 66.1% females) who had paired nasal and nasopharyngeal samples collected upon hospital presentation. The samples were concomitantly tested with the AAZ-LMB COVID-VIRO ALL IN SARS-CoV-2 RDT-Ag and with Cepheid Xpert Xpress SARS-CoV-2 real-time reverse transcription polymerase chain reaction (RT-PCR). RESULTS: The number of subjects with positive RT-PCR results (i.e., mean Ct value <45) was 116 (70.3%), 109 (66.1%) and 86 (52.1%) with mean Ct values <37 and <30, respectively. In all RT-PCR positive samples, COVID-VIRO ALL IN displayed 78.8% agreement, 0.698 sensitivity, 1.000 specificity, 0.583 negative predictive value (NPV) and 1.000 positive predictive value (PPV) compared to RT-PCR. The median Ct value of samples testing positive with COVID-VIRO ALL IN was significantly lower than those testing negative (22.8 vs. 32.2; p<0.001). In samples with high viral load (i.e., Ct value <30), COVID-VIRO ALL IN displayed 92.1% agreement, 0.895 sensitivity, 0.949 specificity, 0.983 NPV and 0.951 PPV compared to RT-PCR. CONCLUSIONS: Although the diagnostic performance of COVID-VIRO ALL IN do not exactly match those of the manufacturer, its high NPV in high viral load samples would enable fast-track and rapid identification of highly contagious subjects.

Clinical performance of Fujirebio Lumipulse G SARSCoV- 2 Ag chemiluminescent immunoassay.

We evaluated the performance of Fujirebio Lumipulse G SARS-CoV-2 Ag chemiluminescent immunoassay. A nasopharyngeal swab was collected from 160 subjects and assayed simultaneously with Fujirebio Lumipulse G SARS-CoV-2 Ag and Altona Diagnostics RealStar SARS-CoV-2 RT-PCR assays. Using 0.60 pg/mL diagnostic threshold, Fujirebio Lumipulse G SARS-CoV-2 Ag displayed 0.88 area under the curve, 0.88 sensitivity and 0.75 specificity compared to molecular testing. The area under the curve increased to 1.00 after excluding samples with low viral load (i.e., cycle threshold values between 25-37). Thus, this chemiluminescent immunoassay could be used for rapid identification of many subjects with high nasopharyngeal SARS-CoV-2 viral load.

Positivization time of a COVID-19 rapid antigen self-test predicts SARS-CoV-2 viral load: a proof of concept.

OBJECTIVES: This proof of concept study was aimed to validate the hypothesis that the time of positivization of SARS-CoV-2 self-performed rapid diagnostic tests (RDTs) may reflect the actual viral load in the specimen. METHODS: A SARS-CoV-2 positive sample with high viral load was diluted and concomitantly assayed with molecular assay (Xpert Xpress SARS-CoV-2) and RDT (COVID-VIRO ALL IN RDT). The (mean cycle threshold; Ct) values and RDT positivization times of these dilutions were plotted and interpolated by calculating the best fit. The parameters of this equation were then used for converting the positivization times into RDT-estimated SARS-CoV-2 Ct values in routine patient samples. RESULTS: The best fit between measured and RDT-estimated Ct values could be achieved with a 2-degree polynomial curve. The RDT-estimated Ct values exhibited high correlation (r=0.996) and excellent Deming fit (y=1.01 × x - 0.18) with measured Ct values. In 30 consecutive patients with positive RDT test, the correlation between RDT positivization time and measured Ct value was r=0.522 (p=0.003). The correlation of RDT-estimated and measured Ct values slightly improved to 0.577 (Deming fit: y=0.44 × x + 11.08), displaying a negligible bias (1.0; 95% CI, -0.2 to 2.2; p=0.105). Concordance of RDT-estimated and measured Ct values at the <20 cut-off was 80%, with 0.84 sensitivity and 0.73 specificity. CONCLUSIONS: This proof of concept study demonstrates the potential feasibility of using RDTs for garnering information on viral load in patients with acute SARS-CoV-2 infection.

Is there a correlation between MOG-associated disorder and SARS-CoV-2 infection?

BACKGROUND AND PURPOSE: Anti-myelin oligodendrocyte glycoprotein antibodies (MOG-Abs) distinguish a group of inflammatory disorders which can be preceded by specific or non-specific infections. A few single cases have been reported in association with SARS-CoV-2 infection, but a specific study on the correlation between COVID-19 and myelin oligodendrocyte glycoprotein (MOG)-associated disorder (MOGAD) has not yet been performed. The aim of this study was to determine the impact of the pandemic on this condition. METHODS: We analysed SARS-CoV-2 serology in patients newly diagnosed with MOGAD (1 August 2020 to 31 May 2021). MOG-Ab-seronegative age- and time-matched subjects were used as controls. SARS-CoV-2 immunoglobulin G (IgG) levels were analysed using an anti-SARS-CoV-2 US Food and Drug Administration-approved ELISA assay and confirmed with a trimeric anti-SARS-CoV-2 S1/S2 IgG immunochemiluminescent test, concomitantly assaying the anti-receptor binding domain (RBD) of spike protein IgG and anti-RBD total Ig. We actually compared the number of cases referred in each of the last 3 years. RESULTS: Presence of SARS-CoV-2 IgG antibodies was more common (12/30, 40%) in MOGAD patients than in controls (6/30, 20%), although the difference was not significant (p = 0.16; odds ratio 2.67, 95% confidence interval 0.85-9.17). The most common clinical presentations of MOGAD SARS-CoV-2-seropositive patients included optic neuritis (n = 6) and myelitis (n = 3). The number of diagnosed cases increased over the last 3 years, in particular, when including cases referred to us before the COVID-19 pandemic, in the initial phase of the first wave and in the late phase of the second wave (n = 9, rate 10.6% in 2019; n = 13, rate 12.3% in 2020; n = 15, rate 14.7% in 2021). CONCLUSION: Our findings provide preliminary data on SARS-CoV-2 as a potential trigger of MOGAD.

Clinical assessment of the Roche SARS-CoV-2 rapid antigen test.

OBJECTIVES: Novel point-of-care antigen assays present a promising opportunity for rapid screening of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections. The purpose of this study was the clinical assessment of the new Roche SARS-CoV-2 Rapid Antigen Test. METHODS: The clinical performance of Roche SARS-CoV-2 Rapid Antigen Test was evaluated vs. a reverse transcription polymerase chain reaction (RT-PCR) laboratory-based assay (Seegene AllplexTM2019-nCoV) in nasopharyngeal swabs collected from a series of consecutive patients referred for SARS-CoV-2 diagnostics to the Pederzoli Hospital (Peschiera del Garda, Verona, Italy) over a 2-week period. RESULTS: The final study population consisted of 321 consecutive patients (mean age, 46 years and IQR, 32-56 years; 181 women, 56.4%), with 149/321 (46.4%) positive for SARS-CoV-2 RNA via the Seegene AllplexTM2019-nCoV Assay, and 109/321 (34.0%) positive with Roche SARS-CoV-2 Rapid Antigen Test, respectively. The overall accuracy of Roche SARS-CoV-2 Rapid Antigen Test compared to molecular testing was 86.9%, with 72.5% sensitivity and 99.4% specificity. Progressive decline in performance was observed as cycle threshold (Ct) values of different SARS-CoV-2 gene targets increased. The sensitivity was found to range between 97-100% in clinical samples with Ct values <25, between 50-81% in those with Ct values between 25 and <30, but low as 12-18% in samples with Ct values between 30 and <37. CONCLUSIONS: The clinical performance of Roche SARS-CoV-2 Rapid Antigen Test is excellent in nasopharyngeal swabs with Ct values <25, which makes it a reliable screening test in patients with high viral load. However, mass community screening would require the use of more sensitive techniques.

Evaluation of three immunochromatographic tests in COVID-19 serologic diagnosis and their clinical usefulness.

Results of three rapid immunochromatographic tests (ICTs) were compared with those obtained with two automated immunoassays for evaluation of their usefulness. One hundred fifty-nine patients and 67 healthy volunteers were included. Different assays demonstrate 41-45% of diagnostic sensitivities and 91-98% of specificities, with substantial agreement (89.3-91.2%), but a high percentage of weak positive results (13-22%) was observed with ICTs. ICTs performances were comparable to those of automated immunoassays. ICTs could have a role as screening approach due to their easy usability. Subjective interpretation, significant rate of uncertain results, uncertainty on viral antigens source are undoubtedly drawbacks.