Efficiency and sensitivity optimization of a protocol to quantify indoor airborne SARS-CoV-2 levels

Abstract

BackgroundDevelopment of methodologies to quantify airborne microorganisms is needed for the prevention and control of risk infections. It is difficult to conclude which is the most efficient and sensitivity strategy to assess airborne SARS-CoV-2 RNA levels given the disparity of results reported in clinical settings.AimTo improve our previously reported method of measuring SARS-CoV-2 RNA levels, was based on bioaerosol collection with a liquid impinger and RNA quantification with droplet digital PCR (ddPCR).MethodsAir samples were collected in COVID-19 patient rooms to assess efficiency and/or sensitivity of different air samplers, liquid collection media and reverse transcriptases (RT).FindingsMineral oil better retains airborne RNA than hydrophilic media without impairing integrity. SARS-CoV-2 ORF1ab target was detected in 80% of the air samples using BioSampler® with mineral oil. No significant differences in effectiveness were obtained with MD8® sampler provided with gelatine membrane filters, but the SARS-CoV-2 copies/m3 air obtained with the latter were lower (28.4±6.1 vs 9±1.7). SuperScript II RT allows the detection of one single SARS-CoV-2 genome RNA molecule by ddPCR with a high efficiency. This was the only RT that allowed the detection of SARS-CoV-2 N1 target in air samples.ConclusionOptimizing collection efficiency and detection sensitivity for quantification od SARS-CoV-2 RNA in indoor air is important to improve our understanding of the microbiological safety of indoor air.