Wastewater monitoring as a supplementary surveillance tool for capturing SARS-COV-2 community spread. A case study in two Greek municipalities

Abstract

A pilot study was conducted from late October 2020 until mid-April 2021, aiming to examine the association between SARS-CoV-2 RNA concentrations in untreated wastewater and recorded COVID-19 cases in two Greek municipalities. A population of Random Forest and Linear Regression Machine Learning models was trained and evaluated incorporating the concentrations of SARS-CoV-2 RNA in 111 wastewater samples collected from the inlets of two Wastewater Treatment Plants, along with physicochemical parameters of the wastewater influent. The model's predictions were adequately associated with the 7-day cumulative cases with the correlation coefficients (after 5-fold cross validation) ranging from 0.754 to 0.960 while the mean relative errors ranged from 30.42% to 59.46%. Our results provide indications that wastewater-based predictions can be applied in diverse settings and in prolonged time periods, although the accuracy of these predictions may be mitigated. Wastewater-based epidemiology can support and strengthen epidemiological surveillance.

Artificial neural network-based estimation of COVID-19 case numbers and effective reproduction rate using wastewater-based epidemiology

“…Although ANN or other machine learning models hold great promise for their application in WBE, only one previous study compared the effectiveness of random forest method with linear regression ( Koureas et al, 2021 ). The study focused on case numbers and both methods provide very high-level accuracy, likely due to the small dataset obtained from two WWTPs.…”

“…The applications of machine learning and artificial intelligent for the COVID-19 pandemic were reviewed for their potentials in treatment, medication, screening, prediction, forecasting, contact tracing, clinical trials, and drug/vaccination process ( Lalmuanawma et al, 2020 ; Mottaqi et al, 2021 ). A recent study used random forest method to predict the daily COVID-19 cases based on square root of viral concentration in wastewater, with or without normalization to chemical oxygen demand, for two wastewater treatment plants ( Koureas et al, 2021 ). The machine learning models showed improvement in comparison to linear regression models, which also have high correlation coefficients between wastewater measurements and cumulative cases around 0.8-0.9 in this study.…”

Year‐long wastewater monitoring for SARS‐CoV‐2 signals in combined and separate sanitary sewers

“…Studies reporting results for multi‐seasonal monitoring that occurred during periods of higher COVID‐19 testing include data from twice weekly sampling at nine wastewater treatment plants (WWTPs) in Ohio (Ai et al, 2021 ), once to five times weekly sampling at 12 WWTPs in Wisconsin (Feng et al, 2021 ), daily sampling at three WWTPs in Nevada (Li et al, 2022 ), and daily sampling at one WWTP in Greece (Galani et al, 2022 ), sampling two WWTPs in Greece (Koureas et al, 2021 ) and Argentina (Barrios et al, 2021 ; Giraud‐Billoud et al, 2021 ). These studies have reported correlations with reported daily cases (Ai et al, 2021 ; Feng et al, 2021 ) as well as rolling averages of 3–7 days (Ai et al, 2021 ), and cumulative cases for 7–20 days (Barrios et al, 2021 ; Koureas et al, 2021 ) in the sewer catchments. The correlations observed were generally consistent across WWTP; however, Feng et al ( 2021 ) noted that one WWTP had weaker correlations with reported cases and different catchment demographics (lower income, student population) were considered a potential explanation.…”

“…While sewer systems are being used as a tool for WBE, these systems were designed to meet other goals (e.g., sanitation and hydraulics) and present multiple challenges when it comes to interpretation of results. Perhaps best studied are methods for normalizing SARS‐CoV‐2 gene copies in sewage to other system flow, fecal viruses (Ai et al, 2021 ; Barrios et al, 2021 ; Feng et al, 2021 ; Wu et al, 2020 ), fecal indicators (Feng et al, 2021 ), and water quality indicators (Koureas et al, 2021 ) to help account for dilution in these systems that collect more than feces and urine. Among the studies that spanned more than one season (i.e., at least 5 months) reported to date, a variety of correlations between wastewater virus concentrations and clinical cases have been reported.…”

“…Among the studies that spanned more than one season (i.e., at least 5 months) reported to date, a variety of correlations between wastewater virus concentrations and clinical cases have been reported. Daily to a range of 3‐ to 20‐day rolling averages of case reports were commonly tested (Ai et al, 2021 ; Barrios et al, 2021 ; Galani et al, 2022 ; Giraud‐Billoud et al, 2021 ; Koureas et al, 2021 ) as well as comparisons to intensive care unit admissions (Galani et al, 2022 ) across systems with a wide range of flow rates (Table 1 ).…”