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Background Environmental surveillance of SARS-CoV-2 via wastewater has become an invaluable tool for population-level surveillance of COVID-19. Built environment sampling may provide a more spatially refined approach for surveillance of COVID-19 in congregate living settings and other high risk settings (e.g., schools, daycares). Methods We conducted a prospective study in 10 long-term care homes (LTCHs) across three cities in Ontario, Canada between September 2021 and May 2022. Floor surfaces were sampled weekly at multiple locations (range 10 to 24 swabs per building) within each building and analyzed for the presence of SARS-CoV-2 using RT-qPCR. The exposure variable was detection of SARS-CoV-2 on floors. The primary outcome was the presence of a COVID-19 outbreak in the week that floor sampling was performed. Results Over the 9-month study period, we collected 3848 swabs at 10 long-term care homes. During the study period, 19 COVID-19 outbreaks occurred with 103 cumulative weeks under outbreak. During outbreak periods, the proportion of floor swabs positive for SARS-CoV-2 was 50% (95% CI: 47-53) with a median quantification cycle of 37.3 (IQR 35.2-38.7). During non-outbreak periods the proportion of floor swabs positive was 18% (95% CI:17-20) with a median quantification cycle of 38.0 (IQR 36.4-39.1). Using the proportion of positive floor swabs for SARS-CoV-2 to predict COVID-19 outbreak status in a given week, the area under the receiver operating curve (AUROC) was 0.85 (95% CI: 0.78-0.92). Using thresholds of ≥10%, ≥30%, and ≥50% of floor swabs positive for SARS-CoV-2 yielded positive predictive values for outbreak of 0.57 (0.49-0.66), 0.73 (0.63-0.81), and 0.73 (0.6-0.83) respectively and negative predictive values of 0.94 (0.87-0.97), 0.85 (0.78-0.9), and 0.75 (0.68-0.81) respectively. Among 8 LTCHs with an outbreak and swabs performed in the antecedent week, 5 had positive floor swabs exceeding 10% at least five days prior to outbreak identification. For 3 of these 5 LTCHs, positivity of floor swabs exceeded 10% more than 10 days before the outbreak being identified. Conclusions Detection of SARS-CoV-2 on floors is strongly associated with COVID-19 outbreaks in LTCHs. These data suggest a potential role for floor sampling in improving early outbreak identification.

Background Environmental surveillance of SARS-CoV-2 via wastewater has become an invaluable tool for population-level surveillance of COVID-19. More highly resolved environmental sampling approaches may also be useful for surveillance. Built environment sampling may provide a spatially refined approach for surveillance of COVID-19 in congregate living settings. Methods We conducted a prospective study of 10 long-term care homes (LTCHs) in both urban and rural settings in Ontario Canada between September 2021 and April 2022. Floor surfaces were sampled weekly at multiple locations within each building and were analyzed for the presence of SARS-CoV-2 using qPCR. The exposure variable was detection of SARS-CoV-2 on floors. The primary outcome was the presence of a COVID-19 outbreak. We calculated the test characteristics of the presence of SARS-CoV-2 on floors for detection of COVID-19 outbreaks. Results We followed 10 LTCHs for 214 cumulative weeks, and collected 3,219 swabs from 183 unique locations. Overall, 15 COVID-19 outbreaks occurred with 74.9 cumulative weeks of outbreaks. During time periods when there were outbreaks of COVID-19 the proportion of floor swabs positive for SaRS-CoV-2 was 50.8% (95% CI: 47.7-53.9). During time periods where there were no outbreaks of COVID-19 the proportion of floor swabs positive was 15.8% (95% CI:14.3-17.3). Using the proportion of positive floor swabs for SARS-CoV-2 to predict COVID-19 outbreak status for a given week, the area under the receiver operating curve was 0.84 (95% CI: 0.76-0.92). Using thresholds of ≥10%, ≥30%, and ≥50%, the prevalence of floor swabs positive for SARS-CoV-2 yielded positive predictive values for outbreak of 0.52 (0.43-0.61), 0.65 (0.53-0.75), and 0.72 (0.58-0.83) respectively, and negative predictive values of 0.93 (0.86-0.97), 0.85 (0.78-0.91), and 0.80 (0.73-0.86) respectively (Figure 1). 13 outbreaks had floor sampling performed in the week prior to them being identified, and of these 7 (54%) had positive swab proportions exceeding 30% in the week prior to the outbreak. Figure 1.Test characteristics of built environment floor swabs for predicting COVID-19 outbreaks in LTCH. Figure 1. Test characteristics of different thresholds for percentage of floor swabs positive for SARS-CoV-2 at a given LTCH for predicting active COVID-19 outbreak in the same building in the same week. NPV = negative predictive value, PPV = positive predictive value, Sens = sensitivity, Spec = specificity. Conclusion Detection of SARS-CoV-2 on floors is strongly associated with COVID-19 outbreaks in LTCHs. These data suggest a potential role for floor sampling in improving early outbreak detection and management. Disclosures Michael Fralick, MD, ProofDx: Advisor/Consultant Doug Manuel, MD, PhD, World Bank: Advisor/Consultant.

Classroom and staffroom floor swabs across six elementary schools in Ottawa, Canada were tested for SARS-CoV-2. Schools in neighbourhoods with historically elevated COVID-19 burden had lower environmental swab positivity. Environmental test positivity did not correlate with student grade groups, school-level absenteeism, pediatric COVID-19-related hospitalizations, or community SARS-CoV-2 wastewater levels.SummaryEnvironmental SARS-CoV-2 sampling was performed in six schools in Ottawa, Canada. The percentage of floor swabs detecting SARS-CoV2 was not correlated with absenteeism, pediatric hospitalizations, or wastewater data. Schools in neighbourhoods with previously elevated COVID-19 rates had lower test positivity.