Head-to-head comparison of direct-input RT-PCR and RT-LAMP against RTqPCR on extracted RNA for rapid SARS-CoV-2 diagnostics

Viral pandemics, such as Covid-19, pose serious threats to human societies. To control the spread of highly contagious viruses such as SARS-CoV-2, effective test-trace-isolate strategies require population-wide, systematic testing. Currently, RT-qPCR on extracted RNA is the only broadly accepted test for SARS-CoV-2 diagnostics, which bears the risk of supply chain bottlenecks, often exaggerated by dependencies on proprietary reagents. Here, we directly compare the performance of gold standard diagnostic RT-qPCR on extracted RNA to direct input RT-PCR, RT-LAMP and bead-LAMP on 384 primary patient samples collected from individuals with suspected Covid-19 infection. With a simple five minute crude sample inactivation step and one hour of total reaction time, we achieve assay sensitivities of 98% (direct RT-PCR), 93% (bead-LAMP) and 82% (RT-LAMP) for clinically relevant samples (diagnostic RT-qPCR Ct <35) and a specificity of >98%. For direct RT-PCR, our data further demonstrate a perfect agreement between real-time and end-point measurements, which allow a simple binary classification similar to the powerful visual readout of colorimetric LAMP assays. Our study provides highly sensitive and specific, easy to implement, rapid and cost-effective alternatives to diagnostic RT-qPCR tests.

Scalable, rapid and highly sensitive isothermal detection of SARS-CoV-2 for laboratory and home testing

Global efforts to combat the Covid-19 pandemic caused by SARS-CoV-2 still heavily rely on RT-qPCR-based diagnostic tests. However, their high cost, moderate throughput and reliance on sophisticated equipment limit widespread implementation. Loop-mediated isothermal amplification after reverse transcription (RT-LAMP) is an alternative detection method that has the potential to overcome these limitations. We present a rapid, robust, sensitive and versatile RT-LAMP based SARS-CoV-2 detection assay. Our forty-minute procedure bypasses a dedicated RNA isolation step, is insensitive to carry-over contamination, and uses a hydroxynaphthol blue (HNB)-based colorimetric readout, which allows robust SARS-CoV-2 detection from various sample types. Based on this assay, we have substantially increased sensitivity and scalability by a simple nucleic acid enrichment step (bead-LAMP), established a pipette-free version for home testing (HomeDip-LAMP), and developed open source enzymes that can be produced in any molecular biology setting. Our advanced, universally applicable RT-LAMP assay is a major step towards population-scale SARS-CoV-2 testing.