SARS-CoV-2 Aggregated Activity Level Across Ontario Canada, Measured with the US CDC Wastewater Viral Activity Level (WVAL) Metric

The wastewater viral activity level (WVAL) was developed by the United States Centers for Disease Control and Prevention (US CDC) as a standardized metric to aggregate SARS-CoV-2 wastewater data, enabling the assessment of infection levels and trends at state/territorial, regional and national scales. This approach also facilitates comparative analysis of SARS-CoV-2 prevalence across regions. In this study, we developed and evaluated graphical methods to integrate the WVAL metric into interpretable visualizations for public health decision-making. Preliminary analysis demonstrated that WVAL values correlated strongly with clinical case counts, supporting its role as a confirmatory epidemiological measure. The WVAL framework provided a linear quantification method, allowing for the comparison of regional variations in infection patterns. This study leveraged data from the Ontario Wastewater Surveillance Initiative (Ontario WSI), which included over 100 sampling sites across seven geographical regions. Weekly mean WVAL values were computed for each site and aggregated at regional and provincial levels. In total, 59 sites contributed to the provincial WVAL calculation. The computational aggregation method followed the US CDC’s WVAL approach and was generally comparable to the Public Health Ontario (PHO) aggregation method, with the notable improvement of incorporating a linear level scale. Overall, this study demonstrated that WVAL effectively quantified SARS-CoV-2 differences at a public health regional scale. The WVAL metric proved to be a robust epidemiological tool, complementing other surveillance measures to support public health decision-making.