Indoor dust as a matrix for surveillance of COVID-19 outbreaks

Ongoing disease surveillance is a critical tool to mitigate viral
outbreaks, especially during a pandemic. Environmental monitoring has
significant promise even following widespread vaccination among high-risk
populations. The goal of this work is to demonstrate molecular SARS-CoV-2
monitoring in bulk floor dust and related samples as a proof-of-concept of
a non-invasive environmental surveillance methodology for COVID-19 and
potentially other viral diseases.  Surface swab, passive sampler,
and bulk floor dust samples were collected from rooms of individuals
infected with COVID-19, and SARS-CoV-2 was measured with quantitative
reverse transcription polymerase chain reaction (RT-qPCR) and two digital
PCR (dPCR) methods. Bulk dust samples had geometric mean concentration of
159 copies/mg-dust and ranged from non-detects to 23,049 copies/mg-dust
detected using ddPCR. An average of 88% of bulk dust samples were positive
for the virus among detection methods compared to 55% of surface swabs and
fewer on the passive sampler (19% carpet, 29% polystyrene). In bulk dust,
SARS-CoV-2 was detected in 76%, 93%, and 97% of samples measured by qPCR,
chip-based dPCR, and droplet dPCR respectively. Detectable viral RNA in
the bulk vacuum bags did not measurably decay over 4 weeks, despite the
application of a disinfectant before room cleaning.  Future
monitoring efforts should further evaluate RNA persistence and
heterogeneity in dust. This study did not measure virus viability in dust
or potential transmission associated with dust. Overall, this work
demonstrates that bulk floor dust is a potentially useful matrix for
long-term monitoring of viral disease outbreaks in high-risk populations
and buildings.