Environmental monitoring has been core to Healthy Davis Together’s (HDT) approach since the program launched in September 2020. Our hypothesis was that environmental monitoring conducted through wastewater testing and supplemented by air and surface sampling, would create a holistic system of early COVID-19 detection. While wastewater testing has allowed us to take definitive action when spikes are detected (residents in affected communities are alerted and encouraged to get tested), air and surface sampling has been less conclusive. This is largely due to the challenge of distinguishing between fresh RNA that could signal recent infection, or relic RNA that is left from a past infection and has remained over time.
The paper “The challenge of SARS-CoV-2 environmental monitoring in schools using floors and portable HEPA filtration units: Fresh or relic RNA?” details our process and findings from an eight-month pilot in 96 classrooms across five schools in Davis, California.
Through deploying and sampling HEPA filters, as well as sampling various surfaces, we were able to detect SARS-CoV-2 RNA in several classrooms. However, intermittent and repeated positives after filters had been changed confirms the challenge of interpreting positive results in previously positive environments, since positive results could be caused by the resuspension and capture of relic RNA on air filters.
This pilot has taught us that while HEPA filter sampling appears to be a more efficient tool compared to floor swabs, more research is needed to determine the utility of this kind of monitoring in schools. One element our team is currently working on are methods to distinguish fresh signals from the relic RNA. Additionally, lessons learned have informed a number of changes to HDT’s current indoor environmental monitoring including a focus on high-touch surfaces, implementation of action thresholds, and modified response protocols.