A colorimetric reverse-transcription loop-mediated isothermal amplification method targeting the L452R mutation to detect the Delta variant of SARS-CoV-2

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has triggered global difficulties for both individuals and economies, with new variants continuing to emerge. The Delta variant of SARS-CoV-2 remains most prevalent worldwide, and it affects the efficacy of coronavirus disease 2019 (COVID-19) vaccination. Expedited testing to detect the Delta variant of SARS-CoV-2 and monitor viral transmission is necessary. This study aimed to develop and evaluate a colorimetric reverse-transcription loop-mediated isothermal amplification (RT-LAMP) technique targeting the L452R mutation in the S gene for the specific detection of the Delta variant. In the test, positivity was indicated as a color change from purple to yellow. The assay's 95% limit of detection was 57 copies per reaction for the L452R (U1355G)-specific standard plasmid. Using 126 clinical samples, our assay displayed 100% specificity, 97.06% sensitivity, and 98.41% accuracy in identifying the Delta variant of SARS-CoV-2 compared to real-time RT-PCR. To our knowledge, this is the first colorimetric RT-LAMP assay that can differentiate the Delta variant from its generic SARS-CoV-2, enabling it as an approach for studying COVID-19 demography and facilitating proper effective control measure establishment to fight against the reemerging variants of SARS-CoV-2 in the future.