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. 2023 Jan 15;856(Pt 1):158964.
doi: 10.1016/j.scitotenv.2022.158964. Epub 2022 Sep 24.

Does normalization of SARS-CoV-2 concentrations by Pepper Mild Mottle Virus improve correlations and lead time between wastewater surveillance and clinical data in Alberta (Canada): comparing twelve SARS-CoV-2 normalization approaches

Rasha Maal-Bared  1 , Yuanyuan Qiu  2 , Qiaozhi Li  2 , Tiejun Gao  2 , Steve E Hrudey  2 , Sudha Bhavanam  2 , Norma J Ruecker  3 , Erik Ellehoj  4 , Bonita E Lee  5 , Xiaoli Pang  6
Affiliations

Does normalization of SARS-CoV-2 concentrations by Pepper Mild Mottle Virus improve correlations and lead time between wastewater surveillance and clinical data in Alberta (Canada): comparing twelve SARS-CoV-2 normalization approaches

Rasha Maal-Bared et al. Sci Total Environ. .

Abstract

Wastewater-based surveillance (WBS) data normalization is an analyte measurement correction that addresses variations resulting from dilution of fecal discharge by non-sanitary sewage, stormwater or groundwater infiltration. No consensus exists on what WBS normalization parameters result in the strongest correlations and lead time between SARS-CoV-2 WBS data and COVID-19 cases. This study compared flow, population size and biomarker normalization impacts on the correlations and lead times for ten communities in twelve sewersheds in Alberta (Canada) between September 2020 and October 2021 (n = 1024) to determine if normalization by Pepper Mild Mottle Virus (PMMoV) provides any advantages compared to other normalization parameters (e.g., flow, reported and dynamic population sizes, BOD, TSS, NH3, TP). PMMoV concentrations (GC/mL) corresponded with plant influent flows and were highest in the urban centres. SARS-CoV-2 target genes E, N1 and N2 were all negatively associated with wastewater influent pH, while PMMoV was positively associated with temperature. Pooled data analysis showed that normalization increased ρ-values by almost 0.1 and was highest for ammonia, TKN and TP followed by PMMoV. Normalization by other parameters weakened associations. None of the differences were statistically significant. Site-specific correlations showed that normalization of SARS-CoV-2 data by PMMoV only improved correlations significantly in two of the twelve systems; neither were large sewersheds or combined sewer systems. In five systems, normalization by traditional wastewater strength parameters and dynamic population estimates improved correlations. Lead time ranged between 1 and 4 days in both pooled and site-specific comparisons. We recommend that WBS researchers and health departments: a) Investigate WWTP influent properties (e.g., pH) in the WBS planning phase and use at least two parallel approaches for normalization only if shown to provide value; b) Explore normalization by wastewater strength parameters and dynamic population size estimates further; and c) Evaluate purchasing an influent flow meter in small communities to support long-term WBS efforts and WWTP management.

Keywords: COVID-19; Combined sewers; Industrial wastewater; Mobile populations; Normalization; Wastewater-based epidemiology (WBE).

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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
Mean SARS-CoV-2 target genes E, N1 and N2 and PMMoV RNA loading (GC/day) in post-grit raw influent samples between May 2020 and October 2021 collected from twelve WWTPs in Alberta. The limit of detection was 80 copies per 100 mL for all three SARS-CoV-2 gene targets (top panel). Bottom panel shows PMMoV concentrations by plant and flow rate (1000 m3/Day).
Fig. 2
Fig. 2
Spearman ρ-values describing the strength of the associations between all normalized and unnormalized, raw SARS-CoV-2 gene targets concentrations (E, N1, N2 and the aaverage of all three) with active and new COVID-19 case rates for all twelve participating wastewater treatment plants (n = 1024). Spearman p-values were all <0.001 and statistically significant.
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