ABSTRACT
Multiplexing has been highlighted to save on costs, increase sample throughput, and maximize on the number of targets that can be sensitively detected within a small sample. With the ongoing SARS-CoV-2 pandemic, different articles have been published highlighting the superiority of droplet digital PCR (ddPCR) over the gold reverse transcription PCR (RT-PCR) in SARS-CoV-2 detection. However, few studies have been reported on developing multiplex ddPCR assays for SARS-CoV-2 detection and their performance. In this study, we developed simplex (1 target), duplex (2 targets), triplex probe mix (3 targets), and fourplex (4 targets) assays based on a two color ddPCR system for SARS-CoV-2 detection. Results showed that the fourplex assay had the similar limits of detection and accuracy to the lower multiplex assays. Analyzing 94 clinical isolates demonstrated that the ddPCR triplex probe mix assay had better sensitivity than the RT-qPCR assay. Additionally, the ddPCR multiplex assay showed that remdesivir could inhibit the growth of SARS-CoV-2 in vitro while another testing drug couldnt. Conclusively, our research shows that developing multiplex ddPCR assays is possible by combing probe mix and amplitude based multiplexing, which will help in developing multiplexed ddPCR assays for different SARS-CoV-2 applications.
ABSTRACT
The ability to detect an infectious agent in a widespread epidemic is crucial to the success of quarantine efforts in addition to sensitive and accurate screening of potential cases of infection from patients in a clinical setting. Enabling testing outside of sophisticated laboratories broadens the scope of control and surveillance efforts, but also requires robust and simple methods that can be used without expensive instrumentation. Here we report a method to identify SARS-CoV-2 (COVID-19) virus RNA from purified RNA or cell lysis using loop-mediated isothermal amplification (LAMP) using a visual, colorimetric detection. This test was additionally verified using RNA samples purified from respiratory swabs collected from COVID-19 patients in Wuhan, China with equivalent performance to a commercial RT-qPCR test while requiring only heating and visual inspection. This simple and sensitive method provides an opportunity to facilitate virus detection in the field without a requirement for complex diagnostic infrastructure.
