Estimating Indoor Airborne Concentrations of SARS-CoV-2

ZOE HOSKIN, Jeffrey Siegel, Sarah R. Haines, University of Toronto

     Abstract Number: 225
     Working Group: Bioaerosols

Abstract
Environmental surveillance of SARS-CoV-2 virus is a critical tool in COVID-19 pandemic recovery efforts. A surveillance method is needed that 1) has less particle size bias than sampling settled dust, 2) is spatially specific to a room within a building, and 3) provides an estimate of airborne concentrations in a room. Therefore, portable air cleaner filters may be leveraged as a tool to assess concentrations of SARS-CoV-2 RNA in indoor spaces using portable air filters and quantitative filter forensics (QFF) techniques. Approximate one-week trials were conducted in residences of covid-symptomatic individuals, classrooms, and community locations in Toronto. Dust from the filters was vacuumed, and then RNA extraction, reverse-transcription-quantitative-polymerase-chain-reaction (RT-qPCR), and digital PCR (dPCR) were performed on the dust samples to quantify SARS-CoV-2 RNA. Metadata from the portable air cleaners was used to determine airborne concentrations of SARS-CoV-2 RNA in each room. The highest airborne concentrations of SARS-CoV-2 RNA in residences were found in the rooms of people who were isolating due to COVID-19 symptoms (ranging from 0.7 to 63.0 RNA copies/m3 air). Disease state (days since symptom onset) may play a role in determining airborne SARS-CoV-2 concentrations in isolation rooms. Other rooms in residences had present, but comparatively low, viral RNA concentrations. Classrooms had low viral concentrations in the summer months when fewer classes were occurring, and higher concentrations during the fall, winter, and spring. Sampling from two filters on different sides of one classroom at the same time revealed very different estimated indoor concentrations of SARS-CoV-2, which may suggest poor air mixing, particularly with respect to localized sources of the virus. In the future, quantitative filter forensics may be applied to building-level surveillance and outbreak-prevention for other airborne viruses.