Current state and future perspectives on de facto population markers for normalization in wastewater-based epidemiology: A systematic literature review

Comparative Assessment of Wastewater-Based Surveillance Normalization Methods to Improve Pathogen Monitoring in Rural Sewersheds

Many in-sewer dynamics that can impact the fidelity of wastewater-based surveillance results remain understudied. Some conventional approaches for normalizing pathogen signals in sewersheds may not be appropriate when there is substantial inflow and infiltration (I&I). Our objective for this study was to evaluate the effect of multiple normalization approaches on wastewater pathogen signals at the WWTP influent and across a small rural sewershed (<3000 people) with different levels of I&I. We collected wastewater samples monthly, from 2022 to 2023, from the wastewater treatment plant (WWTP) influent and 11 additional sewer system nodes with well-characterized I&I impacts. We quantified concentrations of SARS-CoV-2, norovirus GII, and rotavirus at the WWTP influent and subsewershed sites, and compared normalization approaches using flow, population, physicochemical parameters (COD, TSS, NH3(aq), PO43--P), and human fecal markers (crAssphage, HF183, mtDNA). Overall, our findings suggest that in systems with substantial I&I, some commonly used normalization approaches, particularly those using physicochemical parameters, may inadvertently introduce additional variability in viral signals measured at WWTP influent and result in wastewater measures that are more closely associated with precipitation trends rather than with pathogen signals. Normalization with human fecal markers appears to be a relatively robust option for sewersheds impacted by substantial I&I.

Wastewater-based epidemiology of influenza viruses: a systematic review

INTRODUCTION

Wastewater-based epidemiology (WBE) has emerged as a valuable public health tool for monitoring the circulation of many pathogens, including influenza viruses (IVs). The general aim of this study is to systematically retrieve and summarize evidence on the use of WBE for supporting influenza surveillance. Specific objectives are: (i) to map influenza monitoring activities using WBE; (ii) to assess the performance of viral recovery methods; (iii) to explore association with clinical data; (iv) to evaluate the feasibility of typing/subtyping IVs directly from wastewater.

METHODS

We conducted a systematic review following the PRISMA guidelines, focusing on original data from peer-reviewed studies identified through PubMed/Medline, Scopus, and Web of Science.

RESULTS

Of 882 identified citations, 42 studies were included in the review. IVs detection was reported in all but one study, although typically at lower concentration than SARS-CoV-2. Thirteen studies (38.09 %) performed comparative analysis of different protocols, with mostly inconclusive results. Detection of IVs in the solid fraction of wastewater samples generally outperformed detection in the supernatant/liquid. Additionally, we describe the findings from 22 studies (52.38 %) that examined the link between environmental viral concentrations and clinical data, and 14 studies (33.33 %) that described IVs subtyping in wastewater.

CONCLUSION

WBE has the potential to monitor influenza circulation in humans and animals, offering insights into outbreak size and circulating IVs subtypes. However, several key areas remain unexplored. Further research is needed to refine experimental techniques and standardize protocols, and to understand how to successfully integrate WBE data into public health strategies for influenza control.

Advances in Wastewater-Based Epidemiology for Pandemic Surveillance: Methodological Frameworks and Future Perspectives

Wastewater-based epidemiology (WBE) has emerged as a transformative approach for community-level health monitoring, particularly during the COVID-19 pandemic. This review critically examines the methodological framework of WBE systems through the following three core components: (1) sampling strategies that address spatial-temporal variability in wastewater systems, (2) comparative performance of different platforms in pathogen detection, and (3) predictive modeling integrating machine learning approaches. We systematically analyze how these components collectively overcome the limitations of conventional surveillance methods through early outbreak detection, asymptomatic case identification, and population-level trend monitoring. While highlighting technical breakthroughs in viral concentration methods and variant tracking through sequencing, the review also identifies persistent challenges, including data standardization, cost-effectiveness concerns in resource-limited settings, and ethical considerations in public health surveillance. Drawing insights from global implementation cases, we propose recommendations for optimizing each operational phase and discuss emerging applications beyond pandemic response. This review highlights WBE as an indispensable tool for modern public health, whose methodological refinements and cross-disciplinary integration are critical for transforming pandemic surveillance from reactive containment to proactive population health management.

Subsewershed analyses of the impacts of inflow and infiltration on viral pathogens and antibiotic resistance markers across a rural sewer system

As wastewater-based surveillance (WBS) is increasingly used to track community-level disease trends, it is important to understand how pathogen signals can be altered by phenomena that occur within sewersheds such as inflow and infiltration (I&I). Our objectives were to characterize I&I across a rural sewershed and assess potential impacts on viral (rotavirus, norovirus GII, and SARS-CoV-2), fecal indicator (HF183, the hCYTB484 gene specific to the human mitochondrial genome, and crAssphage), and antimicrobial resistance (intI1, blaCTX-M-1) targets. In a small town in Virginia (USA), we collected 107 wastewater samples at monthly intervals over a 12-month period (2022-2023) at the wastewater treatment plant (WWTP) influent and 11 up-sewer sites. Viral, fecal indicator, and antimicrobial resistance targets were enumerated using ddPCR. Physicochemical proxies for organics and nutrient levels in sewage (chemical oxygen demand (COD), total suspended solids (TSS), and NH3(aq)) and genetic markers of anthropogenic impact were used to characterize I&I across the sewershed. Overall, precipitation was negatively associated (Spearman test; ρ < 0; p < 0.01) with physicochemical markers (TSS, COD, K, PO43--P, NH3(aq)) in the WWTP influent. We observed the highest concentrations of human fecal markers and a measure anthropogenic pollution and antibiotic resistance (intI1) in up-sewer sites with limited I&I. However, median viral gene copy concentrations were highest at the WWTP, compared to 100 % (n = 11), 90 % (n = 10), and 55 % (n = 6) of up-sewer sites for rotavirus, norovirus GII, and SARS-CoV-2, respectively. After adjusting for covariates (Ba, COD, dissolved oxygen, groundwater depth, precipitation, sampling date) using generalized linear models, moderate to high I&I was associated with statistically significant reductions in log10-transformed rotavirus and norovirus GII concentrations across the sewershed (coefficients = -0.7 and -0.9, p < 0.001, n = 95), though not for SARS-CoV-2 (coefficient = -0.2, p = 0.181, n = 95). Overall, we found that while I&I can diminish biomarker signals throughout a sewershed, including at the WWTP influent, I&I impacts vary depending on the target, and pathogen biomarker signals were, on average, higher and less variable over time at the WWTP compared to most up-sewer sites. As far as we are aware, this is the first study to assess in situ I&I impacts on multiple WBS targets. Taken together, our findings highlight challenges and tradeoffs associated with different sampling strategies for different WBS targets in heavily I&I impacted systems.

Utilizing national wastewater and sales data to derive and validate the correction factors of five common antidepressants for wastewater-based epidemiology

Monitoring antidepressant use is important for understanding mental health treatment status in populations and detecting potential misuse. Wastewater-based epidemiology (WBE) is a cost-effective approach to conduct such monitoring but requires valid correction factors (CFs) to accurately convert wastewater mass loads into consumption estimates. Most existing CFs are calculated from pharmacokinetic studies with small cohorts and are not specifically validated for WBE purposes. This study aimed to fill this knowledge gap by calibrating and validating the CFs for 5 commonly prescribed antidepressants. CFs were calibrated by dividing corresponding geo-located sales data by wastewater mass loads from 18 wastewater treatment plants in Australia for the same 3.5-year period. The refined CFs were 9.0 for fluoxetine, 6.4 for venlafaxine, and 25 for quetiapine. For the case of racemic citalopram and the pure S-enantiomer (escitalopram), individual CFs were proposed as 2.0 and 11, respectively. To validate their applicability, the new CFs were applied to independent datasets of wastewater samples collected in Belgium (2019 to 2022) and Australia (2020) and compared with sales data. The new calibrated CFs produced more accurate wastewater-based estimates of consumption for citalopram, escitalopram, fluoxetine, venlafaxine, and quetiapine, enhancing the capability of WBE in public health surveillance.

Ketamine, a new (or old) kid on the block: A comprehensive three-year spatio-temporal study in Belgium through wastewater-based epidemiology

Based on reports of ketamine seizures, self-reported consumption and harmful associated health effects, there are signs of increased ketamine use. However, monitoring population-level consumption patterns remains difficult. This study employed wastewater-based epidemiology (WBE) to address this challenge by analysing influent wastewater (IWW) from Belgium for biomarkers of ketamine consumption to evaluate spatio-temporal trends. Daily 24-h composite IWW samples were collected from 26 locations across the northern part of Belgium (Flanders and Brussels region), every Monday and Wednesday in 2023 (n = 716). Additionally, a temporal dataset from daily IWW samples from Leuven (n = 399) and Brussels (n = 285) in 2021 and 2022 was evaluated using time series analysis. Measured concentrations of ketamine, norketamine and dehydronorketamine in IWW were transformed to population-normalised mass loads (PNML, expressed in mg/day/1000 inhabitants) to assess ketamine consumption patterns. Ketamine, norketamine and dehydronorketamine were detected in respectively 98%, 96%, and 76% of all samples. Substantial consumption was observed in both urban and rural areas, with higher PNMLs in major cities and the east of Flanders. Temporal analysis showed no seasonal trends but an increase in weekend consumption, likely linked to recreational use. PNMLs increased 7- to 11-fold compared to available data in 2012. Actual consumption and direct disposal down the drain could be differentiated by the investigation of the ketamine to norketamine ratio. Ketamine use is widespread across the north of Belgium, encompassing a relatively stable, year-round consumption. In future WBE studies, it is recommended to measure both norketamine and ketamine to assess ketamine consumption and to rule out any dumping events.

Evaluating Population Normalization Methods Using Chemical Data for Wastewater-Based Epidemiology: Insights from a Site-Specific Case Study

Wastewater-based epidemiology (WBE) has been widely employed to track the spread of human pathogens; however, correlating wastewater data with clinical surveillance remains challenging due to population variability and environmental factors affecting wastewater composition. This study evaluated different SARS-CoV-2 normalization methods, comparing static population estimates with dynamic normalization based on common physicochemical parameters: chemical oxygen demand (COD), biochemical oxygen demand (BOD5), and ammonia (NH4-N). Wastewater samples were collected from four urban wastewater treatment plants (WWTPs) in northwestern Tuscany (Italy) from February 2021 to March 2023. The correlations between normalized viral loads and clinical COVID-19 cases were highest for static normalization (ρ = 0.405), followed closely by dynamic normalization using COD and BOD5 (ρ = 0.378 each). Normalization based on NH4-N was less effective. These findings suggest that chemical parameters, particularly COD and BOD5, offer a valid alternative for viral normalization when population estimates or flow rate measurements are unavailable. These parameters provide a cost-effective and practical approach for improving WBE reliability, particularly in resource-limited settings. Our results reinforce the importance of normalization in WBE to enhance its representativeness and applicability for public health surveillance.

Evaluating the potential of wastewater-based epidemiology to estimate the retail illicit drug market size in Europe: A case study

BACKGROUND AND AIMS

Estimating the retail drug market size is complex due to its clandestine nature, yet useful for intervention and policy planning. Wastewater-based epidemiology (WBE) offers an alternative strategy to estimate population-wide consumption trends by analysing influent wastewater, avoiding self-reporting biases associated with other estimation techniques, e.g., consumption or expenditure-based models. This study evaluates the applicability of WBE for drug market size estimation.

METHODS

Using WBE data the drug market situation of amphetamine, cocaine, MDMA, and methamphetamine is estimated in European cities (n=75) through combination with price/purity information (Statistical Bulletin) published by the European Union Drugs Agency. Market sizes were estimated at three levels: (L1) pure drug quantities, (L2) adulterated retail drugs quantities, and (L3) market value. Furthermore, yearly consumption estimates from the commonly applied consecutive seven-day sampling is compared to a randomised stratified sampling approach in Brussels, Belgium.

RESULTS

Challenges include the availability and accuracy of price and purity data, which complicates cross-country comparisons and hinders the higher-levels calculations. Due to missing data, the market value (L3) could only be calculated for a limited number of cities, i.e., 39% (amphetamine), 39% (cocaine), 1% (MDMA), and 23% (methamphetamine). Furthermore, statistically significant differences were shown for amphetamine (up to 139% measurement error) and methamphetamine (up to 58% measurement error) between both sampling approaches.

CONCLUSIONS

Particularly at city level, WBE can complement traditional market size estimations, but significant uncertainties remain. Future research should expand one-week consecutive sampling to a randomised stratified sampling approach tailored to drug and location.

Wastewater-Based Epidemiological Surveillance in France: The SUM'EAU Network

Wastewater surveillance is a powerful public health tool which gained global prominence during the COVID-19 pandemic. This article describes the development and implementation of the national wastewater surveillance network in France: SUM'EAU. Preliminary work included defining a sampling strategy, evaluating/optimising analytical methods, launching a call for tenders to select network laboratories and producing wastewater monitoring indicators. SUM'EAU was then deployed in three stages: (i) a pilot study, (ii) the transfer of analytical activities from the National Reference Laboratory to four selected network laboratories, and (iii) the extension of the system to additional sampling sites. Currently, SUM'EAU monitors SARS-CoV-2 across 54 wastewater treatment plants in mainland France. Once a week on business days, 24 h flow-proportional composite samples are collected at plant inlets and transported at 5 °C (±3 °C) to partner laboratories for analysis. The analytical process involves sample concentration, RNA extraction, and digital RT-PCR/q-RT-PCR to detect and quantify the presence of the SARS-CoV-2 genome in wastewater. Subsequently, data are transferred to Santé publique France, the French National Public Health Agency, for analysis and interpretation. While SUM'EAU has been instrumental in monitoring the COVID-19 pandemic and holds significant potential for broader application, securing sustainable funding for its operation remains a major challenge.

Wastewater Surveillance of SARS-CoV-2 in Slovenia: Key Public Health Tool in Endemic Time of COVID-19

With the reclassification of COVID-19 as an endemic disease and the relaxation of measures, Slovenia needed a complementary system for monitoring SARS-CoV-2 infections. This article provides an overview of the epidemiological situation of SARS-CoV-2 in Slovenia using a wastewater surveillance system, demonstrating its usefulness as a complementary tool in epidemiological surveillance. This study found that estimated SARS-CoV-2 infections in Slovenia peaked in September 2022 and showed a declining trend with subsequent lower peaks in March-April and December 2023, mirroring the trends observed from clinical data. Based on both surveillance systems, the most prevalent variant in 2022 was BA.5. By 2023, BQ.1 and other Omicron variants increased in prevalence. By the end of 2023, XBB sublineages and the BA.2.86 variant had become predominant, demonstrating consistent dynamic shifts in variant distribution across both monitoring methods. This study found that wastewater surveillance at wastewater treatment plants in Slovenia effectively tracked SARS-CoV-2 infection trends, showing a moderate to strong correlation with clinical data and providing early indications of changes in infection trends and variant emergence. Despite limitations during periods of low virus concentration, the system proved significant in providing early warnings of infection trends and variant emergence, thus enhancing public health response capabilities.