SLAMP: A Rapid Fluorometric RT-LAMP Assay for Sensitive and Specific Detection of SARS-CoV-2 from Human Saliva

Rapid testing methods can identify outbreaks and trigger preventive strategies for slowing the spread of SARS-CoV-2, the virus that causes COVID-19. The gold-standard detection method for SARS-CoV-2 is reverse transcription quantitative polymerase chain reaction (RT-qPCR) performed on samples collected using a nasopharyngeal (NP) swab. While NP RT-qPCR provides high sensitivity, it requires trained personnel to administer and suffers from lengthy time-to-result. Recently, the testing community has turned to rapid saliva-based screening methods including saliva-to-RT-qPCR and/or saliva-to-RT-LAMP (reverse transcription loop-mediated isothermal amplification) to identify infected individuals regardless of symptomatic presentation. Here, we report a simple and rapid RT-LAMP fluorometric assay performed directly on heat-inactivated saliva, without the addition of buffers or proteinase K treatments we call saliva LAMP (SLAMP). Over the course of two days, a total of 243 individuals were tested using NP RT-qPCR, saliva-based qPCR, and saliva-based RT-LAMP. Of the 243 NP RT-qPCR tests, 65 were positive, 178 were negative, and SLAMP demonstrated a 91% sensitivity and 98% specificity. SLAMP sensitivity becomes 95% when samples negative in saliva tests while positive in NP RT-qPCR are excluded from evaluation, potentially indicating significant differences in viral titer between collection sites on the body. SLAMP is performed in triplicates and takes 45 min to run in the laboratory, requiring less technician time and instrument run time than NP RT-qPCR. These results demonstrate that saliva-based RT-LAMP can enable frequent and rapid screening of large numbers of people to identify pre-symptomatic and asymptomatic individuals thereby controlling outbreaks.