OBJECTIVES:

Site-specific wastewater surveillance could potentially control COVID-19 outbreaks more effectively at long-term care facilities (LTCF). It could identify the presence of pre-symptomatic and asymptomatic COVID-19 infections in the facility and therefore initiate timely outbreak control measures. Besides, compared to repetitive screenings of residents and staff using diagnostic tests, screenings based on positive wastewater test results incur fewer costs and less discomfort. We evaluated the effectiveness of LTCF-site-specific wastewater surveillance in preventing COVID-19 outbreaks, by comparing the scenario where more diagnostic tests were initiated due to positive wastewater test results and the base case of no action.

METHODS:

We built a susceptible-infected-cases-recovered model to study COVID-19 transmission at LTCF under the base-case and wastewater surveillance scenario. We used data from an outbreak during the Omicron wave in one LTCF in Edmonton, Canada (December 2021 – March 2022), where wastewater data did not initiate actions. We fit base-case model parameters with daily cases and testing data using the nonlinear least-squares method. We hypothesized 10%-50% more diagnostic tests in the wastewater scenario. We compared the outbreak size, i.e., predicted numbers of infections, to measure the effectiveness. We used the Mann-Whitney U test to identify whether the outbreak size in the wastewater scenario was significantly smaller.

RESULTS:

Results reported are subject to minor changes as modelling work is ongoing. The number of infections peaked on day 25 in the base case, with 23.8% of individuals being infected. In the wastewater scenario, all hypothesized values resulted in a significantly smaller outbreak size; only 10% more diagnostic tests could lead to 5.4% fewer infections (p=0.03) at the peak.

CONCLUSIONS:

This pilot study demonstrates the potential effectiveness of LTCF-site-specific wastewater surveillance to prevent COVID-19 outbreaks. Future works include engaging policymakers in analyzing specific wastewater-based actions and estimating the costs of controlling COVID-19 to explore the cost-effectiveness of wastewater surveillance.