Seroprevalence of SARS-CoV-2 infection in health care workers of a teaching hospital in Belgium: self-reported occupational and household risk factors for seropositivity.

This study aims to evaluate SARS-CoV-2 seroprevalence among health care workers (HCWs) and to assess self-reported risk factors for seropositivity. A total of 3255 HCWs were included and the overall seroprevalence was 7.8%. The likelihood of seropositivity was higher in participants reporting any COVID-19 symptoms within the last 4 months (OR 8.32, 95% CI 5.83-11.88, P < 0.001). Being a female HCW (OR 1.32, 95% CI 1.11-2.32, P < 0.01), having a cohabitant who was infected with SARS-CoV-2 (OR 2.55, 95% CI 1.78-3.66 P < 0.001) or a cohabitant who was a nursing home caregiver (OR 3.71, 95% CI 1.59-8.65, P = 0.002) were independently associated with an increased risk of seropositivity. Working in a COVID-19 unit (OR 1.64, 95% CI 1.21-2.23, P < 0.001) and being exposed to a SARS-CoV-2 infected co-worker (OR 1.30,95% CI 0.97-1.74, P = 0.016) resulted in higher seropositivity rate. Even if in-hospital exposure may play a significant role, increased infection risk is most likely attributable to household contact.

How to choose the right real-time RT-PCR primer sets for the SARS-CoV-2 genome detection?

OBJECTIVES: The SARS-CoV-2 pandemic has created an unprecedented need for rapid large-scale diagnostic testing to prompt clinical and public health interventions. Currently, several quantitative reverse-transcription polymerase chain reaction (RT-qPCR) assays recommended by the World Health Organization are being used by clinical and public health laboratories and typically target regions of the RNA-dependent RNA polymerase (RdRp), envelope (E) and nucleocapsid (N) coding region. However, it is currently unclear if results from different tests are comparable. This study aimed to clarify the clinical performances of the primer/probe sets designed by US CDC and Charité/Berlin to help clinical laboratories in assay selection for SARS-CoV-2 routine detection. METHODS: We compared the clinical performances of the recommended primer/probe sets using one hundred nasopharyngeal swab specimens from patients who were clinically diagnosed with COVID-19. An additional 30 "pre-intervention screening" samples from patients who were not suspected of COVID-19 were also included in this study. We also performed sequence alignment between 31064 European SARS-CoV-2 and variants of concern genomes and the recommended primer/probe sets. RESULTS: The present study demonstrates substantial differences in SARS-CoV-2 RNA detection sensitivity among the primer/probe sets recommended by the World Health Organization especially for low-level viral loads. The alignment of thousands of SARS-CoV-2 sequences reveals that the genetic diversity remains relatively low at the primer/probe binding sites. However, multiple nucleotide mismatches might contribute to false negatives. CONCLUSION: An understanding of the limitations depending on the targeted genes and primer/probe sets may influence the selection of molecular detection assays by clinical laboratories.

Clinical usefulness of fully automated chemiluminescent immunoassay for quantitative antibody measurements in COVID-19 patients.

Since December 2019, we have been in the battlefield with a new threat to the humanity, known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), characterized by viral pneumonia. It may be asymptomatic or cause various symptoms, ranging from flu-like symptoms to acute respiratory distress syndrome and eventually death. At present, the only reliable test for COVID-19 diagnosis is quantitative reverse transcriptase-polymerase chain reaction. Assessing the immune response against SARS-CoV-2 could increase the detection sensitivity of infected population. Hereby, we report the performances of a fully automated chemiluminescent immunoassay (CLIA) on 276 serum samples. One hundred samples obtained from COVID-19 negative subjects (COVID-19 free) were analyzed to evaluate the diagnostic specificity of antibody (Ab) detection. Thereafter, 176 samples obtained from 125 patients with confirmed COVID-19 (COVID-19 patients) were selected to assess the diagnostic sensitivity of the CLIA. All samples were analyzed on MAGLUMI 800 platform. All COVID-19 free samples had Ab levels below the cutoff values. Hence, the diagnostic specificity was estimated at 100% (95% confidence interval [CI] = 96.3-100.0; positive predictive value = 100%). By the 18th day from the onset of symptoms, we reached an optimal diagnostic sensitivity (more than 95.0%) In fact, the diagnostic sensitivity increased over time and between 15 and 25 days after symptoms onset, reached 95.5% (95% CI = 84.9-99.2). The new automated CLIA analyzer appeared to be a robust and reliable method to measure specific Ab against COVID-19 at high throughput. Our data suggest that combining Ab and nucleic acid detection could increase diagnostic sensitivity.

Usefulness of a multiplex immunodot in case of discordant results between automated COVID-19 serological assays.

BACKGROUND: At present, the only reliable test for COVID-19 diagnosis is RT-qPCR. Serological assays have been widely used to increase the detection sensitivity of infected population. Hereby, we report the performance of a new pan-IgG multiplex Enzyme Immunoassay (immunodot) method for exploration of discrepant SARS-COV-2 serological results. METHODS: A retrospective study on 38 residual serum samples from recovered COVID-19 subjects with discordant serological results on Roche and Snibe platforms, were reanalyzed on a new semi-automated pan-IgG immunodot Enzyme Immunoassay, namely COVIDOT-TEST, in order to find the source of discrepancies and to evaluate the latter method. All samples were analyzed on the BlueDiver® Instrument and all strips were read by the BlueScan® Scanner using Dr DOT® Software. RESULTS: Based on our data, subject samples showed specific IgG reactions on ≥ 2 different antigens on immunodot strips. Of these 38 samples, 97.4 % of samples showed specific IgG reaction against S1 + S2 antigens, 89.5 % showed against RBD antigen, 86.8 % against S2 antigen reaction on the COVIDOT-TEST kit. Specific IgG-S1 antigen and IgG-N antigen reactions were detected in 73.7 % and 65.8 % of the samples, respectively. CONCLUSION: The new semi-automated pan-IgG immunodot Enzyme Immunoassay method appeared to be a reliable assay to confirm suspicious COVID-19 serological screening results.

Low performance of rapid antigen detection test as frontline testing for COVID-19 diagnosis.

BACKGROUND: Ensuring accurate diagnosis is essential to limit the spread of SARS-CoV-2 and for the clinical management of COVID-19. Although real-time reverse transcription polymerase chain reaction (RT- qPCR) is the current recommended laboratory method to diagnose SARS-CoV-2 acute infection, several factors such as requirement of special equipment and skilled staff limit the use of these time-consuming molecular techniques. Recently, several easy to perform rapid antigen detection tests were developed and recommended in some countries as the first line of diagnostic. OBJECTIVES: The aim of this study was to evaluate the performances of the Coris COVID-19 Ag Respi-Strip test, a rapid immunochromatographic test for the detection of SARS-CoV-2 antigen, in comparison to RT-qPCR. RESULTS: 148 nasopharyngeal swabs were tested. Amongst the 106 positive RT-qPCR samples, 32 were detected by the rapid antigen test, given an overall sensitivity of 30.2%. All the samples detected positive with the antigen rapid test were also positive with RT-qPCR. CONCLUSIONS: Higher viral loads are associated with better antigen detection rates. Unfortunately, the overall poor sensitivity of the COVID-19 Ag Respi-Strip does not allow using it alone as the frontline testing for COVID-19 diagnosis.