Researcher handling test tubes in a laboratory_lab

A 14-month program in Canadian long-term care facilities has found that floor swabs accurately detect a COVID-19 outbreak days before it is identified by staff members.

Floor surfaces were sampled weekly across 10 facilities between September 2021 and November 2022. Swabbing targeted multiple locations within each building. Investigators analyzed the samples for the presence of SARS-CoV-2 and compared the timing of the swabs and with COVID-19 outbreaks.

Half of floor swabs positive

The researchers, who collected 4,895 swabs, found that 23 COVID-19 outbreaks occurred during the study period, with 119 cumulative weeks under outbreak status. During outbreaks, more than half (54%) of floor swabs were positive for SARS-CoV-2. That proportion was 22% during non-outbreak periods, reported Derek R. MacFadden, MD ScD, of the University of Ottawa.

When an outbreak occurred, eight of the 10 participating facilities had floor swabs performed in the prior week that exceeded 10% positivity for SARS-CoV-2 at least five days before the outbreak was identified. In addition, seven of the facilities had swabs with 10% positivity more than 10 days before the outbreak was recognized.

Once the outbreaks resolved, floor swab positivity for SARS-CoV-2 declined, MacFadden and colleagues reported. 

Floor samples and early treatment

The results suggest that “built environment SARS-CoV-2 testing could be a valuable tool for identifying and monitoring SARS-CoV-2 outbreaks in long-term care homes,” the authors wrote. Floor sampling has high accuracy, likely because COVID-19 spreads through respiratory particles that may settle to the floor surface, and could facilitate early treatment of disease, they noted.

Full findings were published in the New England Journal of Medicine, Evidence.

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