Comparison of the Ct-values for genomic and subgenomic SARS-CoV-2 RNA reveals limited predictive value for the presence of replication competent virus.

SARS-CoV-2 is the causative agent of the acute respiratory disease COVID-19. In addition to the full length positive-sensed, single-stranded genomic RNA (gRNA), viral subgenomic RNAs (sgRNAs) that are required for expression of the 3' region of the genome are synthesized in virus-infected cells. However, whether these sgRNA-species might be used as a measure of active virus replication and to predict infectivity is still under debate. The commonly used methods to monitor and quantitate SARS-CoV-2 infections are based on RT-qPCR analysis and the detection of gRNA. The infectivity of a sample obtained from nasopharyngeal or throat swabs is associated with the viral load and inversely correlates with Ct-values, however, a cut-off value predicting the infectivity highly depends on the performance of the assay. Furthermore, gRNA derived Ct-values result from nucleic acid detection and do not necessarily correspond to active replicating virus. We established a multiplex RT-qPCR assay on the cobas 6800 omni utility channel concomitantly detecting SARS-CoV-2 gRNAOrf1a/b, sgRNAE,7a,N, and human RNaseP-mRNA used as human input control. We compared the target specific Ct-values with the viral culture frequency and performed ROC curve analysis to determine the assay sensitivity and specificity. We found no advantage in the prediction of viral culture when using sgRNA detection compared to gRNA only, since Ct-values for gRNA and sgRNA were highly correlated and gRNA offered a slightly more reliable predictive value. Single Ct-values alone only provide a very limited prediction for the presence of replication competent virus. Hence, careful consideration of the medical history including symptom onset has to be considered for risk stratification.

Is Olfactory Testing a Useful Diagnostic Tool to Identify SARS-CoV-2 Infections Early? A Cross-Sectional and Longitudinal Analysis.

BACKGROUND: Genesis and the prognostic value of olfactory dysfunction (OD) in COVID-19 remain partially described. The objective of our study was to characterize OD during SARS-CoV-2 infection and to examine whether testing of OD may be a useful tool in clinical practice in order to early identify patients with SARS-CoV-2 infection. METHODS: Olfactory function assessment was objectively carried out using the u-Smell-it® test. In a cross-sectional study part, we evaluated this test in a control cohort of SARS-CoV-2 negative tested patients, who attended the University Hospital Frankfurt between May 2021 and March 2022. In a second longitudinal study part, sensitivity and specificity of OD was evaluated as a diagnostic marker of a SARS-CoV-2 infection in Frankfurt am Main, Germany in SARS-CoV-2 infected patients and their close contacts. RESULTS: Among 494 SARS-CoV-2 negative tested patients, OD was detected in 45.7% and was found to be significantly associated with the male gender (p < 0.001), higher age (p < 0.001), cardiovascular and pulmonary comorbidities (p < 0.001; p = 0.03). Among 90 COVID-19 positive patients, OD was found in 65.6% and was significantly associated with male gender and positive smoking status (p = 0.04 each). Prevalence and severity of OD were significantly increased in infections with the Delta variant (B.1.617.2) compared to those with the Omicron variant (BA.1.1.529). Diagnostic sensitivity and specificity of OD for diagnosis of SARS-CoV-2 infection were 69% and 64%, respectively. CONCLUSION: OD is common in COVID-19 negative and positive tested patients with significantly different prevalence rates observed between different variants. Diagnostic accuracy of OD is not high enough to implement olfactory testing as a tool in diagnostic routine to early identify patients with a SARS-CoV-2 infection.

RNA reference materials with defined viral RNA loads of SARS-CoV-2-A useful tool towards a better PCR assay harmonization.

SARS-CoV-2, the cause of COVID-19, requires reliable diagnostic methods to track the circulation of this virus. Following the development of RT-qPCR methods to meet this diagnostic need in January 2020, it became clear from interlaboratory studies that the reported Ct values obtained for the different laboratories showed high variability. Despite this the Ct values were explored as a quantitative cut off to aid clinical decisions based on viral load. Consequently, there was a need to introduce standards to support estimation of SARS-CoV-2 viral load in diagnostic specimens. In a collaborative study, INSTAND established two reference materials (RMs) containing heat-inactivated SARS-CoV-2 with SARS-CoV-2 RNA loads of ~107 copies/mL (RM 1) and ~106 copies/mL (RM 2), respectively. Quantification was performed by RT-qPCR using synthetic SARS-CoV-2 RNA standards and digital PCR. Between November 2020 and February 2021, German laboratories were invited to use the two RMs to anchor their Ct values measured in routine diagnostic specimens, with the Ct values of the two RMs. A total of 305 laboratories in Germany were supplied with RM 1 and RM 2. The laboratories were requested to report their measured Ct values together with details on the PCR method they used to INSTAND. This resultant 1,109 data sets were differentiated by test system and targeted gene region. Our findings demonstrate that an indispensable prerequisite for linking Ct values to SARS-CoV-2 viral loads is that they are treated as being unique to an individual laboratory. For this reason, clinical guidance based on viral loads should not cite Ct values. The RMs described were a suitable tool to determine the specific laboratory Ct for a given viral load. Furthermore, as Ct values can also vary between runs when using the same instrument, such RMs could be used as run controls to ensure reproducibility of the quantitative measurements.

Self-Collected Samples to Detect SARS-CoV-2: Direct Comparison of Saliva, Tongue Swab, Nasal Swab, Chewed Cotton Pads and Gargle Lavage.

Testing for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) by RT-PCR is a vital public health tool in the pandemic. Self-collected samples are increasingly used as an alternative to nasopharyngeal swabs. Several studies suggested that they are sufficiently sensitive to be a useful alternative. However, there are limited data directly comparing several different types of self-collected materials to determine which material is preferable. A total of 102 predominantly symptomatic adults with a confirmed SARS-CoV-2 infection self-collected native saliva, a tongue swab, a mid-turbinate nasal swab, saliva obtained by chewing a cotton pad and gargle lavage, within 48 h of initial diagnosis. Sample collection was unsupervised. Both native saliva and gargling with tap water had high diagnostic sensitivity of 92.8% and 89.1%, respectively. Nasal swabs had a sensitivity of 85.1%, which was not significantly inferior to saliva (p = 0.092), but 16.6% of participants reported they had difficult in self-collection of this sample. A tongue swab and saliva obtained by chewing a cotton pad had a significantly lower sensitivity of 74.2% and 70.2%, respectively. Diagnostic sensitivity was not related to the presence of clinical symptoms or to age. When comparing self-collected specimens from different material, saliva, gargle lavage or mid-turbinate nasal swabs may be considered for most symptomatic patients. However, complementary experiments are required to verify that differences in performance observed among the five sampling modes were not attributed to collection impairment.

Longitudinal Testing for Respiratory and Gastrointestinal Shedding of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Day Care Centers in Hesse, Germany.

BACKGROUND: With the pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) ongoing in Europe in June 2020, day care centers were reopened in the state of Hesse, Germany, after the lockdown. The role young children play in the dynamics of the transmission was unknown. METHODS: We conducted a longitudinal study over 12 weeks and 2 days (18 June 2020-10 September 2020) to screen attendees and staff from day care centers in the state of Hesse, Germany, for both respiratory and gastrointestinal shedding of SARS-CoV-2. A total of 859 children (age range, 3 months-8 years) and 376 staff members from 50 day care centers, which were chosen representatively from throughout the state, participated in the study. Parents were asked to collect both a buccal mucosa and an anal swab from their children once a week. Staff were asked to self-administer the swabs. Reverse transcriptas polymerase chain reaction for SARS-CoV-2 was performed in a multiple-swab pooling protocol. RESULTS: A total of 7366 buccal mucosa swabs and 5907 anal swabs were analyzed. No respiratory or gastrointestinal shedding of SARS-CoV-2 was detected in any of the children. Shedding of SARS-CoV-2 was detected in 2 staff members from distinct day care centers. One was asymptomatic at the time of testing, and one was symptomatic and did not attend the facility on that day. CONCLUSION: Detection of either respiratory or gastrointestinal shedding of SARS-CoV-2 RNA in children and staff members attending day care centers was rare in the context of limited community activity and with infection prevention measures in the facilities in place.

COVID-19 among children seeking primary paediatric care with signs of an acute infection.

AIM: It can be challenging to distinguish COVID-19 in children from other common infections. We set out to determine the rate at which children consulting a primary care paediatrician with an acute infection are infected with SARS-CoV-2 and to compare distinct findings. METHOD: In seven out-patient clinics, children aged 0-13 years with any new respiratory or gastrointestinal symptoms and presumed infection were invited to be tested for SARS-CoV-2. Factors that were correlated with testing positive were determined. Samples were collected from 25 January 2021 to 01 April 2021. RESULTS: Seven hundred and eighty-three children participated in the study (median age 3 years and 0 months, range 1 month to 12 years and 11 months). Three hundred and fifty-eight were female (45.7%). SARS-CoV-2 RNA was detected in 19 (2.4%). The most common symptoms in children with as well as without detectable SARS-CoV-2 RNA were rhinitis, fever and cough. Known recent exposure to a case of COVID-19 was significantly correlated with testing positive, but symptoms or clinical findings were not. CONCLUSION: COVID-19 among the children with symptoms of an acute infection was uncommon, and the clinical presentation did not differ significantly between children with and without evidence of an infection with SARS-CoV-2.

Novel multiple swab method enables high efficiency in SARS-CoV-2 screenings without loss of sensitivity for screening of a complete population.

BACKGROUND: In the pandemic, testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by real-time polymerase chain reaction is one of the pillars on which countermeasures are based. Factors limiting the output of laboratories interfere with the effectiveness of public health measures. Conserving reagents by pooling samples in low-probability settings is proposed but may cause dilution and loss of sensitivity. Blood transfusion services had experience in performance of high throughput nucleic acid testing (NAT) analysis and can support the national health system by screening of the inhabitants for SARS-COV-2. METHODS: We evaluated a new approach of a multiple-swab method by simultaneously incubating multiple respiratory swabs in a single tube. Analytical sensitivity was constant up to a total number of 50 swabs. It was consequently applied in the testing of 50 symptomatic patients (5-sample pools) as well as 100 asymptomatic residents of a nursing home (10-sample pools). RESULTS: The novel method did not cause false-negative results with nonsignificantly differing cycle threshold values between single-swab and multiple-swab NAT. In two routine applications, all minipools containing positive patient samples were correctly identified. CONCLUSIONS: The new method enables countries to increase the total number of testing significantly. The multiple-swab method is able to screen system relevant groups of employees frequently. The example in Germany shows that blood transfusion services can support general health systems with their experience in NAT and their high-throughput instruments. Screening of a huge number of inhabitants is currently the only option to prevent a second infection wave and enable exit strategies in many countries.

Surveillance of SARS-CoV-2 in Frankfurt am Main from October to December 2020 Reveals High Viral Diversity Including Spike Mutation N501Y in B.1.1.70 and B.1.1.7.

BACKGROUND: International travel is a major driver of the introduction and spread of SARS-CoV-2. AIM: To investigate SARS-CoV-2 genetic diversity in the region of a major transport hub in Germany, we characterized the viral sequence diversity of the SARS-CoV-2 variants circulating in Frankfurt am Main, the city with the largest airport in Germany, from the end of October to the end of December 2020. METHODS: In total, we recovered 136 SARS-CoV-2 genomes from nasopharyngeal swab samples. We isolated 104 isolates that were grown in cell culture and RNA from the recovered viruses and subjected them to full-genome sequence analysis. In addition, 32 nasopharyngeal swab samples were directly sequenced. RESULTS AND CONCLUSION: We found 28 different lineages of SARS-CoV-2 circulating during the study period, including the variant of concern B.1.1.7 (Δ69/70, N501Y). Six of the lineages had not previously been observed in Germany. We detected the spike protein (S) deletion Δ69/Δ70 in 15% of all sequences, a four base pair (bp) deletion (in 2.9% of sequences) and a single bp deletion (in 0.7% of sequences) in ORF3a, leading to ORF3a truncations. In four sequences (2.9%), an amino acid deletion at position 210 in S was identified. In a single sample (0.7%), both a 9 bp deletion in ORF1ab and a 7 bp deletion in ORF7a were identified. One sequence in lineage B.1.1.70 had an N501Y substitution while lacking the Δ69/70 in S. The high diversity of sequences observed over two months in Frankfurt am Main highlights the persisting need for continuous SARS-CoV-2 surveillance using full-genome sequencing, particularly in cities with international airport connections.

Typical symptoms of common otorhinolaryngological diseases may mask a SARS-CoV-2 infection.

PURPOSE: Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) replicates predominantly in the upper respiratory tract and is primarily transmitted by droplets and aerosols. Taking the medical history for typical COVID-19 symptoms and PCR-based SARS-CoV-2 testing have become established as screening procedures. The aim of this work was to describe the clinical appearance of SARS-CoV-2-PCR positive patients and to determine the SARS-CoV-2 contact risk for health care workers (HCW). METHODS: The retrospective study included n = 2283 SARS-CoV-2 PCR tests from n = 1725 patients with otorhinolaryngological (ORL) diseases performed from March to November 2020 prior to inpatient treatment. In addition, demographic data and medical history were assessed. RESULTS: n = 13 PCR tests (0.6%) were positive for SARS-CoV-2 RNA. The positive rate showed a significant increase during the observation period (p < 0.01). None of the patients had clinical symptoms that led to a suspected diagnosis of COVID-19 before PCR testing. The patients were either asymptomatic (n = 4) or had symptoms that were interpreted as symptoms typical of the ORL disease or secondary diagnoses (n = 9). CONCLUSION: The identification of SARS-CoV-2-positive patients is a considerable challenge in clinical practice. Our findings illustrate that taking a medical history alone is of limited value and cannot replace molecular SARS-CoV-2 testing, especially for patients with ORL diseases. Our data also demonstrate that there is a high probability of contact with SARS-CoV-2-positive patients in everyday clinical practice, so that the use of personal protective equipment, even in apparently "routine cases", is highly recommended.

Comparative analysis of point-of-care, high-throughput and laboratory-developed SARS-CoV-2 nucleic acid amplification tests (NATs).

Multiple nucleic acid amplification tests (NATs) are available for the detection of SARS-CoV-2 in clinical specimens, including Laboratory Developed Tests (LDT), commercial high-throughput assays and point-of-care tests. Some assays were just recently released and there is limited data on their clinical performance. We compared the Xpert® Xpress SARS-CoV-2 (Cepheid) and Vivalytic VRI Panel (Schnelltest COVID-19) (Bosch) point-of-care tests with four high-throughput assays and one LDT, the cobas® SARS-CoV-2 test (Roche), the Allplex™ 2019-nCoV Assay (Seegene), the SARS-CoV-2 AMP (Abbott) Kit, the RealStar® SARS-CoV-2 RT-PCR Kit 1.0 (altona) as well as an assay using a SARS-CoV-2 RdRP gene specific primer and probe set. Samples from patients with confirmed SARS-CoV-2 infection, samples from the first and second SARS-CoV-2-PCR External Quality Assessment (EQA) (INSTAND e.V.) and a 10-fold serial dilution of a SARS-CoV-2 cell culture (SARS-CoV-2 Frankfurt 1) supernatant were examined. We determined that the NAT assays examined had a high specificity. Assays using the N gene as target demonstrated the highest sensitivity in the serial dilution panel, while all examined NAT assays showed a comparable sensitivity when testing clinical and EQA samples.

The Comparative Clinical Performance of Four SARS-CoV-2 Rapid Antigen Tests and Their Correlation to Infectivity In Vitro.

Due to globally rising numbers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections, resources for real-time reverse-transcription polymerase chain reaction (rRT-PCR)-based testing have been exhausted. In order to meet the demands of testing and reduce transmission, SARS-CoV-2 antigen-detecting rapid diagnostic tests (Ag-RDTs) are being considered. These tests are fast, inexpensive, and simple to use, but whether they detect potentially infectious cases has not been well studied. We evaluated three lateral flow assays (RIDA®QUICK SARS-CoV-2 Antigen (R-Biopharm), SARS-CoV-2 Rapid Antigen Test (Roche)), and NADAL® COVID-19 Ag Test (Nal von Minden GmbH, Regensburg, Germany) and one microfluidic immunofluorescence assay (SARS-CoV-2 Ag Test (LumiraDx GmbH, Cologne, Germany)) using 100 clinical samples. Diagnostic rRT-PCR and cell culture testing as a marker for infectivity were performed in parallel. The overall Ag-RDT sensitivity for rRT-PCR-positive samples ranged from 24.3% to 50%. However, for samples with a viral load of more than 6 log10 RNA copies/mL (22/100), typically seen in infectious individuals, Ag-RDT positivity was between 81.8% and 100%. Only 51.6% (33/64) of the rRT-PCR-positive samples were infectious in cell culture. In contrast, three Ag-RDTs demonstrated a more significant correlation with cell culture infectivity (61.8-82.4%). Our findings suggest that large-scale SARS-CoV-2 Ag-RDT-based testing can be considered for detecting potentially infective individuals and reducing the virus spread.

Optimized qRT-PCR Approach for the Detection of Intra- and Extra-Cellular SARS-CoV-2 RNAs.

The novel coronavirus SARS-CoV-2 is the causative agent of the acute respiratory disease COVID-19, which has become a global concern due to its rapid spread. Meanwhile, increased demand for testing has led to a shortage of reagents and supplies and compromised the performance of diagnostic laboratories in many countries. Both the World Health Organization (WHO) and the Center for Disease Control and Prevention (CDC) recommend multi-step RT-PCR assays using multiple primer and probe pairs, which might complicate the interpretation of the test results, especially for borderline cases. In this study, we describe an alternative RT-PCR approach for the detection of SARS-CoV-2 RNA that can be used for the probe-based detection of clinical isolates in diagnostics as well as in research labs using a low-cost SYBR green method. For the evaluation, we used samples from patients with confirmed SARS-CoV-2 infections and performed RT-PCR assays along with successive dilutions of RNA standards to determine the limit of detection. We identified an M-gene binding primer and probe pair highly suitable for the quantitative detection of SARS-CoV-2 RNA for diagnostic and research purposes.

Multicentre comparison of quantitative PCR-based assays to detect SARS-CoV-2, Germany, March 2020.

Containment strategies and clinical management of coronavirus disease (COVID-19) patients during the current pandemic depend on reliable diagnostic PCR assays for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Here, we compare 11 different RT-PCR test systems used in seven diagnostic laboratories in Germany in March 2020. While most assays performed well, we identified detection problems in a commonly used assay that may have resulted in false-negative test results during the first weeks of the pandemic.

Ad hoc laboratory-based surveillance of SARS-CoV-2 by real-time RT-PCR using minipools of RNA prepared from routine respiratory samples.

BACKGROUND: A novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerged in China in late 2019 and subsequently caused a pandemic. Surveillance is important to better appreciate this evolving pandemic and to longitudinally monitor the effectiveness of public health measures. OBJECTIVES: We aimed to provide a rapid, easy to establish and costeffective laboratory-based surveillance tool for SARS-CoV-2. STUDY DESIGN: We used minipools of RNA prepared from nucleic acid extractions of routine respiratory samples. We technically validated the assay and distributed the protocol within an informal network of five German university laboratories. RESULTS: We tested a total of 70 minipools resembling 700 samples shortly before the upsurge of cases in Germany from 17.02.2020 to 10.03.2020. One minipool reacted positive and after resolution one individual sample tested SARS-CoV-2 positive. This sample was from a hospitalized patient not suspected of having contracted SARS-CoV-2. CONCLUSIONS: Our approach of a laboratory-based surveillance for SARSCoV-2 using minipools proved its concept is easily adaptable and resource-saving. It might assist not only public health laboratories in SARS-CoV-2 surveillance.