The Omicron variant BQ.1* with mutations at positions 28,311 and 28,312 in the SARS-CoV-2 N gene have minimal impact on CDC N1 target detection (preprint)

Ensuring COVID-19 testing remains accurate and reliable is of critical importance as the SARS-CoV-2 virus continues to evolve. Currently, a number of Omicron variants are dominating infection across the globe in including BQ.1 and XBB. Both variants and their sublineages (BQ.1* and XBB*) contain a 28,311 C/U mutation inherited from the original Omicron variant (BA.1). This mutation overlaps with a commonly used fluorescent probe for N gene detection in many Emergency Use Authorization (EUA) assays, as this target was originally established by the U.S. Centers for Disease Control and Prevention (CDC) in their EUA test for COVID-19 (2019-nCoV_N1). This C to U mutation was previously shown to have no impact on CDC N1 target detection. The rise of Omicron sublineages has increased the likelihood of additional point mutations occurring within the same assay target. A subpopulation of BQ.1* has an additional 28,312 C/U mutation within the CDC 2019_nCoV_N1 fluorescent probe in addition to the 28,311 C/U mutation. The double mutation could adversely affect the ability of diagnostic assays to detect the virus in patient samples and therefore it is important to verify the impacts of this additional mutation. Using in vitro transcribed (IVT) N gene RNA representing the wildtype (GenBank/GISAID ID MN908947.3 ) and Omicron BQ.1.1 variant (BQ.1, GISAID ID EPI_ISL_ 15155651), we evaluated the performance of two different amplification protocols, both of which include the CDC 2019-nCoV_N1 primer-probe set. Both assays successfully detected the mutant N gene sequence efficiently even at 10 copies of input, although the double mutation caused a 0.5~1 Cq delay on average when compared to the wild-type sequence. These data suggest that circulating BQ.1* lineage viruses with this double mutation likely have minimal impact on diagnostic assays that use the 2019-nCoV-N1 primer-probe.

Development and Implementation of a Simple and Rapid Extraction-Free Saliva SARS-CoV-2 RT-LAMP Workflow for Workplace Surveillance (preprint)

Effective management of the COVID-19 pandemic requires widespread and frequent testing of the population for SARS-CoV-2 infection. Saliva has emerged as an attractive alternative to nasopharyngeal samples for surveillance testing as it does not require specialized personnel or materials for its collection and can be easily provided by the patient. We have developed a simple, fast, and sensitive saliva-based testing workflow that requires minimal sample treatment and equipment. After sample inactivation, RNA is quickly released and stabilized in an optimized buffer, followed by reverse transcription loop-mediated isothermal amplification (RT-LAMP) and detection of positive samples using a colorimetric and/or fluorescent readout. The workflow was optimized using 1,670 negative samples collected from 172 different individuals over the course of 6 months. Each sample was spiked with 50 copies/L of inactivated SARS-CoV-2 virus to monitor the efficiency of viral detection. Using pre-defined clinical samples, the test was determined to be 100% specific and 97% sensitive, with a limit of detection comparable to commercially available RT-qPCR-based diagnostics. The method was successfully implemented in a CLIA laboratory setting for workplace surveillance and reporting. From April 2021-February 2022, more than 30,000 self-collected samples from 755 individuals were tested and 85 employees tested positive mainly during December and January, consistent with high infections rates in Massachusetts and nationwide. The rapid identification and isolation of infected individuals with trace viral loads before symptom onset minimized viral spread in the workplace.

Enhancing Colorimetric LAMP Amplification Speed and Sensitivity with Guanidine Chloride (preprint)

Loop-mediated isothermal amplification (LAMP) is a versatile technique for detection of target DNA and RNA, enabling rapid molecular diagnostic assays with minimal equipment. The global SARS-CoV-2 pandemic has presented an urgent need for new and better diagnostic methods, with colorimetric LAMP utilized in numerous studies for SARS-CoV-2 detection. However, the sensitivity of colorimetric LAMP in early reports has been below that of the standard RT-qPCR tests, and we sought to improve performance. Here we report the use of guanidine hydrochloride and combined primer sets to increase speed and sensitivity in colorimetric LAMP, bringing this simple method up to the standards of sophisticated technique and enabling accurate and high-throughput diagnostics.