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. 2023 Jun 10:876:162800.
doi: 10.1016/j.scitotenv.2023.162800. Epub 2023 Mar 11.

A wastewater-based risk index for SARS-CoV-2 infections among three cities on the Canadian Prairie

Mohsen Asadi  1 , Femi F Oloye  2 , Yuwei Xie  3 , Jenna Cantin  3 , Jonathan K Challis  3 , Kerry N McPhedran  4 , Warsame Yusuf  5 , David Champredon  5 , Pu Xia  3 , Chantel De Lange  3 , Seba El-Baroudy  3 , Mark R Servos  6 , Paul D Jones  7 , John P Giesy  8 , Markus Brinkmann  9
Affiliations

A wastewater-based risk index for SARS-CoV-2 infections among three cities on the Canadian Prairie

Mohsen Asadi et al. Sci Total Environ. .

Abstract

Wastewater surveillance (WWS) is useful to better understand the spreading of coronavirus disease 2019 (COVID-19) in communities, which can help design and implement suitable mitigation measures. The main objective of this study was to develop the Wastewater Viral Load Risk Index (WWVLRI) for three Saskatchewan cities to offer a simple metric to interpret WWS. The index was developed by considering relationships between reproduction number, clinical data, daily per capita concentrations of virus particles in wastewater, and weekly viral load change rate. Trends of daily per capita concentrations of SARS-CoV-2 in wastewater for Saskatoon, Prince Albert, and North Battleford were similar during the pandemic, suggesting that per capita viral load can be useful to quantitatively compare wastewater signals among cities and develop an effective and comprehensible WWVLRI. The effective reproduction number (Rt) and the daily per capita efficiency adjusted viral load thresholds of 85 × 106 and 200 × 106 N2 gene counts (gc)/population day (pd) were determined. These values with rates of change were used to categorize the potential for COVID-19 outbreaks and subsequent declines. The weekly average was considered 'low risk' when the per capita viral load was 85 × 106 N2 gc/pd. A 'medium risk' occurs when the per capita copies were between 85 × 106 and 200 × 106 N2 gc/pd. with a rate of change <100 %. The start of an outbreak is indicated by a 'medium-high' risk classification when the week-over-week rate of change was >100 %, and the absolute magnitude of concentrations of viral particles was >85 × 106 N2 gc/pd. Lastly, a 'high risk' occurs when the viral load exceeds 200 × 106 N2 gc/pd. This methodology provides a valuable resource for decision-makers and health authorities, specifically given the limitation of COVID-19 surveillance based on clinical data.

Keywords: COVID-19 outbreak; Clinical data; Effective reproduction number; Epidemiology; Risk index; Wastewater surveillance.

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Conflict of interest statement

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Unlabelled Image
Graphical abstract
Fig. 1
Fig. 1
Time series of the 7-day moving average of efficiency-adjusted viral RNA loads and 15 points smoothed clinical data in Saskatoon (since the Alpha wave), Prince Albert, and North Battleford (both since the Delta waves).
Fig. 2
Fig. 2
Daily per capita SARS-CoV-2 viral loads for Saskatoon (violet), Prince Albert (blue), and North Battleford (black) during Delta (left side of the panel) and Omicron (right side of the panel) waves of the COVID-19 pandemic. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 3
Fig. 3
Real-time smoothed effective reproduction number (solid red lines) and daily per capita SARS-CoV-2 viral loads (solid blue lines) for Saskatoon, Prince Albert, and North Battleford during Delta (left side of the panel) and Omicron (right side of the panel) waves of the COVID-19 pandemic. Two horizontal navy-blue dash lines indicate the threshold viral loads of 85 × 106 (--) and 200 × 106 (-.) N2 gc/pd., respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 4
Fig. 4
Wastewater Viral Load Risk Index (WWWVLRI) performance during the COVID-19 pandemic Alpha wave for Saskatoon, and Delta and Omicron waves for Saskatoon, Prince Albert, and North Battleford. Black bars represent the percentage rate of change week-over-week, and the colour bars represent weekly averages of daily viral loads (three measurements weekly) with associated risks. (For interpretation of the references to colour in this figure, the reader is referred to the web version of this article.)
See this image and copyright information in PMC

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