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

Abstract

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.

Keywords: COVID-19; France; SARS-CoV-2; SUM’EAU; epidemiology; public health; surveillance; wastewater.

Figure 1

Selection process for sampling sites based on the size of the area (criterion A), geographic coverage on the departmental scale (criterion B), and the capacity of the WWTP (criterion C). UU: Urban Unit; WWTP: wastewater treatment plant; kg: kilogram; PE: population equivalent.

Figure 2

Percentage of the population covered per department by the 126 WWTPs selected for the SUM’EAU network.

Figure 3

SUM’EAU implementation stages. WWTP: wastewater treatment plant; WWS: wastewater surveillance.

Figure 4

Summary of SUM’EAU’s wastewater indicators production process. * NH₄-N: ammonium expressed in mg/L of ammonium (NH₄) as nitrogen (N). § Genome concentration of SARS-CoV-2 determined using the E gene target for quantification and a second target (N1, N2, or IP4) for confirmation.

Figure 5

Ratio of E gene concentrations measured by the National Reference Laboratory to those measured by the four network laboratories.

Figure 6

Comparison between three sources of epidemiological data: (i) normalised SARS-CoV-2 concentrations in wastewater (WWI) (represented by the pink line), (ii) COVID-19 incidence rates (Ti) (represented by the green dashed line), and (iii) OSCOUR^® indicators, for 12 wastewater treatment plants (represented by the blue histograms). WWTP: wastewater treatment plant; WWI: wastewater indicator—ratio of viral concentration of SARS-CoV-2 to concentration of ammonium nitrogen; Ti: incidence rate per 100,000 inhabitants; OSCOUR^®: number of emergency room visits associated with suspected COVID-19 per 100 visits; W: week.

Figure 7

Correlations between the wastewater indicator and two epidemiological indicators: incidence rate (Ti) and OSCOUR^® emergency room visits attributed to SARS-CoV-2 rate per 100,000 people. WWI: wastewater indicator—ratio of viral concentration of SARS-CoV-2 to concentration of ammonium nitrogen; OSCOUR^®: proportion of emergency room visits associated with COVID-19 per 100 visits; Ti: incidence rate per 100,000 inhabitants; W: week.