Adaptation of the multiplexed CRISPR-Cas13 CARMEN RVP assay for longitudinal detection of respiratory pathogens from...

Air sampling is a non-invasive alternative to individual testing for respiratory pathogens. Alternative methods to the "gold standard" quantitative RT-PCR (qRT-PCR) are required to enable higher throughput, lower cost, and more multiplexed detection of pathogens. The multiplexed CRISPR-Cas13 CARMEN Respiratory Viral Panel (RVP) was described previously for high-throughput detection of nine respiratory pathogens from nasal swab samples. Here, we modified and optimized the CARMEN RVP assay to overcome the unique challenges of air samples, including low biomass and environmental inhibitors. We monitored for SARS-CoV-2 and influenza A (Flu A) via qRT-PCR in air samples from 15 schools within Dane County, Wisconsin (USA) during the 2023-2024 school year. SARS-CoV-2 was detectable throughout the entire sampling period, while Flu A detection was seasonal from November 2023 to March 2024. We then analyzed a subset of samples from seven schools using an optimized CARMEN RVP assay for air surveillance (RVP_air) and compared results to qRT-PCR. The RVP_air assay detected several additional pathogens beyond our primary targets. The frequencies and patterns of SARS-CoV-2 positivity, but not Flu A, were similar between qRT-PCR and RVP_air across the 2023-2024 sampling period. We developed a secondary panel (RVP_air_flu) to better detect both H1N1 and H3N2 subtypes. Finally, we compared air sample results to clinical nasal swabs collected from the same school district. For several pathogens (SARS-CoV-2, HCoV-OC43, Flu A), positive air detections coincided with positive nasal swabs. These findings demonstrate that the RVP_air assay can effectively detect airborne pathogens from infected individuals within indoor spaces.