RESUMO
BackgroundSARS-CoV-2 can be detected from the built environment (e.g., floors), but it is unknown how the viral burden changes over space and time surrounding an infected patient. Characterising these data can help advance our understanding and interpretation of surface swabs from the built environment. MethodsWe conducted a prospective study at two hospitals in Ontario, Canada between January 19, 2022 and February 11, 2022. We performed serial floor sampling for SARS-CoV-2 in rooms of patients newly hospitalized with COVID-19 in the past 48 hours. We sampled the floor twice daily until the occupant moved to another room, was discharged, or 96 hours had elapsed. Floor sampling locations included: 1m from the hospital bed, 2m from the hospital bed, and at the rooms threshold to the hallway (typically 3 - 5m from the hospital bed). The samples were analyzed for the presence of SARS-CoV-2 using qPCR. We calculated the sensitivity of detecting SARS-CoV-2 in a patient with COVID-19, and we evaluated how the percentage of positive swabs and the cycle threshold of the swabs changed over time. We also compared the cycle threshold between the two hospitals. ResultsOver the 6-week study period we collected 164 floor swabs from the rooms of 13 patients. The overall percentage of swabs positive for SARS-CoV-2 was 93% and the median cycle threshold (for positive swabs) was 33.7 (IQR: 30.9, 37.5). On day 0 of swabbing the percentage of swabs positive for SARS-CoV-2 was 81.1% and the median cycle threshold was 33.7 (IQR: 32.1, 38.3) compared to swabs performed on day 2 or later where the percentage of swabs positive for SARS-CoV-2 was 98.1% and the cycle threshold was 33.4 (IQR: 30.7, 35.7). We found that viral detection did not change with increasing time (since the first sample collection) over the sampling period, OR 1.65 per day (95% CI 0.68, 4.02; p = 0.27). Similarly, viral detection did not change with increasing distance from the patients bed (1m, 2m, or 3m), OR 0.85 per metre (95% CI 0.38, 1.88; p = 0.69). The cycle threshold was lower (e.g. more virus) in The Ottawa Hospital (median Cq 30.8) where the floors are cleaned once daily rather than the Toronto hospital (median Cq 37.3) where floors were cleaned twice daily. ConclusionsWe were able to detect SARS-CoV-2 on the floors of rooms of patients with COVID-19 and the viral burden did not vary over time or by distance from the bed. These results suggest floor swabbing for the detection of SARS-CoV-2 in a built environment such as a hospital room is both accurate and robust to variation in sampling location and duration of occupancy.
RESUMO
BackgroundEnvironmental 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). MethodsWe 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. ResultsOver 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. ConclusionsDetection 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.
