Environmental SARS-CoV-2 Detection — Bringing It Inside

Wastewater sampling to detect SARS-CoV-2 is useful for confirming the prevalence of this virus in communities that share a disposal system — and in some cases, positive findings have preceded clinical presentation of the disease (NEJM JW Infect Dis Jun 2022 and Emerg Infect Dis 2022 Apr 22; [e-pub]). The benefits of this approach include noninvasiveness and relatively low cost. However, the pooled sampling of wastewater precludes identification of specific loci of infection. Now, Canadian researchers have taken this sampling approach closer to individual outbreak sites. From September 2021 through November 2022, floors of 10 long-term care (LTC) facilities were sampled weekly (4895 swabs) for SARS-CoV-2 RNA and records of predefined COVID-19 outbreaks were noted. Swabs were obtained in general resident-use areas and not in individual living spaces. Sampling of ambient CO₂ levels (a measure of ventilation) was performed in the same areas.

During outbreaks, swab positivity rates rose to 54% from a baseline of 22% (for samples collected between outbreaks). Eight LTCs had elevated sample positivity rates >5 days prior to an outbreak and seven had increased likelihood of positive swabs >10 days prior. There was no correlation of outbreaks or floor positivity with ambient CO₂ levels.