Environmental surveillance for SARS-CoV-2 for outbreak detection in hospital: A single centre prospective study (preprint)

Identifying COVID-19 outbreaks in hospitals at an early stage requires active surveillance. Our objective was to assess whether floor swabs correlated with COVID-19 outbreak status in hospital. We swabbed the floors of an inpatient ward at Mount Sinai Hospital for 32 weeks, from October 31, 2022 to June 15, 2023 and RT-qPCR analysis provided a quantification cycle of detection for each positive swab. 182 swabs were processed for SARS CoV-2, of which 98.4% were positive. Two COVID-19 outbreaks were declared during the study period. The median viral copy number was 210 (IQR, 49 to 1018) during non-outbreak periods and 653 (IQR, 300 to 1754) during outbreak periods. Analyzing the number of viral copies of SARS-CoV-2, instead of percentage positivity, gave a clearer view of changes in outbreak status over time, thereby illustrating the benefits of this approach to monitor pathogen load in hospital settings.

Detection of SARS-CoV-2 in Schools Using Built Environment Testing in Ottawa, Canada: A Multi-Facility Prospective Surveillance Study (preprint)

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.

Characterizing responsiveness to the COVID-19 pandemic in the United States and Canada using mobility data (preprint)

Background: Mobile phone-derived human mobility data are a proxy for disease transmission risk and have proven useful during the COVID-19 pandemic for forecasting cases and evaluating interventions. We propose a novel metric using mobility data to characterize responsiveness to rising case rates. Methods: We examined weekly reported COVID-19 incidence and retail and recreation mobility from Google Community Mobility Reports for 50 U.S. states and nine Canadian provinces from December 2020 to November 2021. For each jurisdiction, we calculated the responsiveness of mobility to COVID-19 incidence when cases were rising. Responsiveness across countries was summarized using subgroup meta-analysis. We also calculated the correlation between the responsiveness metric and the reported COVID-19 death rate during the study period. Findings: Responsiveness in Canadian provinces ({beta} = -1.45; 95% CI: -2.45, -0.44) was approximately five times greater than in U.S. states ({beta} = -0.30; 95% CI: -0.38, -0.21). Greater responsiveness was moderately correlated with a lower reported COVID-19 death rate during the study period (Spearman's {rho} = 0.51), whereas average mobility was only weakly correlated the COVID-19 death rate (Spearman's {rho} = 0.20). Interpretation: Our study used a novel mobility-derived metric to reveal a near-universal phenomenon of reductions in mobility subsequent to rising COVID-19 incidence across 59 states and provinces of the U.S. and Canada, while also highlighting the different public health approaches taken by the two countries. Funding: This study received no funding.

The association between diabetes and mortality among patients hospitalized with COVID-19: Cohort Study of Hospitalized Adults in Ontario, Canada and Copenhagen, Denmark (preprint)

Importance: Diabetes has been reported to be associated with an increased risk of death among patients with COVID-19. However, available studies lack detail on COVID illness severity and measurement of relevant comorbidities. Design, Setting, and Participants: We conducted a multicenter, retrospective cohort study of patients over the age of 18 years who were hospitalized with COVID-19 between January 1, 2020 and November 30, 2020 in Ontario, Canada and Copenhagen, Denmark. Chart abstraction emphasizing co-morbidities and disease severity was performed by trained research personnel. The association between diabetes and death was measured using Poissson regression. Main Outcomes and Measures: within hospital 30-day risk of death. Results: Our study included 1018 hospitalized patients with COVID-19 in Ontario and 305 in Denmark, of whom 405 and 75 patients respectively had pre-existing diabetes. In both Ontario and Denmark, patients with diabetes were more likely to be older, have chronic kidney disease, cardiovascular disease, higher troponin levels, and to receive antibiotics compared with adults who did not have diabetes. In Ontario, the crude mortality rate ratio among patients with diabetes was 1.60 [1.24 -- 2.07 95% CI] and in the adjusted regression model was 1.20 [0.86 -- 1.66 95% CI]. In Denmark, the crude mortality rate ratio among patients with diabetes was 1.27 (0.68 -- 2.36 95% CI) and in the adjusted model was 0.90 (0.49 -- 1.54 95% CI)]. Meta-analyzing the two rate ratios from each region resulted in a crude mortality rate ratio of 1.55 (95% CI 1.22,1.96) and an adjusted mortality rate ratio of 1.11 (95% CI 0.84, 1.47). Conclusions: Presence of diabetes was not strongly associated with in-hospital COVID mortality independent of illness severity and other comorbidities.

Increased Interregional Travel to Shopping Malls and Restaurants in Response to Differential COVID-19 Restrictions in the Greater Toronto Area (preprint)

Background: In the fall of 2020, the government of Ontario, Canada adopted a 5-tier, regional framework of public health measures for the COVID-19 pandemic. During the second wave of COVID-19 in Ontario, the urban core of the Greater Toronto Area (Toronto and Peel) were the first regions in the province to enter the highest restriction tier ("lockdown") on November 23, 2020, which closed restaurants to in-person dining and limited non-essential businesses, including shopping malls, to curbside pickup. The peripheral regions of the Greater Toronto Area (York, Durham, Halton) would not enter lockdown until later the following month. In this analysis, we examine whether the implementation of differentially timed restrictions in a highly interconnected metropolitan area led to increased interregional travel, potentially driving further transmission of SARS-CoV-2. Methods: We used anonymized smartphone data to estimate the number of visits by residents of regions in the urban core to shopping malls and restaurants in peripheral regions in the week before compared to the week after the November 23 lockdown. Results: Residents of Toronto and Peel took fewer trips to shopping malls and restaurants in the week following lockdown. This was entirely driven by reductions in visits within the locked down regions themselves, as there was a significant increase in trips to shopping malls in peripheral regions by these residents in the same period (Toronto: +40.7%, Peel: +65.5%). Visits to restaurants in peripheral regions also increased slightly (Toronto: +6.3%, Peel: +11.8%). Discussion: Heterogeneous restrictions may undermine lockdowns in the urban core as well as driving residents from zones of higher transmission to zones of lower transmission. These concerns are likely generalizable to other major metropolitan areas, which often comprise interconnected but administratively independent regions.

The mobility gap: estimating mobility levels required to control Canada's winter COVID-19 surge (preprint)

Background Non-pharmaceutical interventions remain a primary means of suppressing COVID-19 until vaccination coverage is sufficient to achieve herd immunity. We used anonymized smartphone mobility measures in seven Canadian provinces to quantify the mobility level needed to suppress COVID-19 (mobility threshold), and the difference relative to current mobility levels (mobility gap). Methods We conducted a longitudinal study of weekly COVID-19 incidence from March 15, 2020 to January 16, 2021, among provinces with 20 COVID-19 cases in at least 10 weeks. The outcome was weekly growth rate defined as the ratio of current cases compared to the previous week. We examined the effects of average time spent outside the home (non-residential mobility) in the prior three weeks using a lognormal regression model accounting for province, season, and mean temperature. We calculated the COVID-19 mobility threshold and gap. Results Across the 44-week study period, a total of 704,294 persons were infected with COVID-19. Non-residential mobility dropped rapidly in the spring and reached a median of 36% (IQR: 31,40) in April 2020. After adjustment, each 5% increase in non-residential mobility was associated with a 9% increase in the COVID-19 weekly growth rate (ratio=1.09, 95%CI: 1.07,1.12). The mobility gap increased through the fall months, which was associated with increasing case growth. Interpretation Mobility strongly and consistently predicts weekly case growth, and low levels of mobility are needed to control COVID-19 through winter 2021. Mobility measures from anonymized smartphone data can be used to guide the provincial and regional implementation and loosening of physical distancing measures.

Estimating the effect of physical distancing on the COVID-19 pandemic using an urban mobility index (preprint)

Background: Governments have implemented population-wide physical distancing measures to control COVID-19, but metrics evaluating their effectiveness are not readily available. Methods: We used a publicly available mobility index from a popular transit application to evaluate the effect of physical distancing on infection growth rates and reproductive numbers in 40 jurisdictions between March 23 and April 12, 2020. Findings: A 10% decrease in mobility was associated with a 14.6% decrease (exp({beta}) = 0.854; 95% credible interval: 0.835, 0.873) in the average daily growth rate and a -0.061 (95% CI: -0.071, -0.052) change in the instantaneous reproductive number two weeks later. Interpretation: Our analysis demonstrates that decreases in urban mobility were predictive of declines in epidemic growth. Mobility metrics offer an appealing method to calibrate population-level physical distancing policy and implementation, especially as jurisdictions relax restrictions and consider alternative physical distancing strategies. Funding: No external funding was received for this study.