Implementation of environmental surveillance for SARS-CoV-2 virus to support public health decisions: Opportunities and challenges

Abstract

Analysing wastewater can be used to track infectious disease agents that are shed via stool and urine. Sewage surveillance of SARS-CoV-2 has been suggested as a tool to determine the extent of COVID-19 in cities and serve as an early warning for (re-)emergence of SARS-CoV-2 circulation in communities. The focus of this review is on the strength of evidence, opportunities and challenges for the application of sewage surveillance to inform public health decision making. Considerations for undertaking sampling programs are reviewed including sampling sites, strategies, sample transport, storage and quantification methods; together with the approach and evidence base for quantifying prevalence of infection from measured wastewater concentration. Published SARS-CoV-2 sewage surveillance studies (11 peer reviewed and 10 preprints) were reviewed to demonstrate the current status of implementation to support public health decisions. Although being very promising, a number of areas were identified requiring additional research to further strengthen this approach and take full advantage of its potential. In particular, design of adequate sampling strategies, spatial and temporal resolution of sampling, sample storage, replicate sampling and analysis, controls for the molecular methods used for the quantification of SARS-CoV-2 RNA in wastewater. The use of appropriate prevalence data and methods to correlate or even translate SARS-CoV-2 concentrations in wastewater to prevalence of virus shedders in the population is discussed.

Keywords: COVID-19; SARS-CoV-2; SSewage surveillance; Wastewater; Wastewater-based epidemiology.

Graphical abstract

Figure 1

The reporting pyramid of COVID-19. The base holds all infections with COVID-19 in the population, both symptomatic and asymptomatic. This base contributes to the SARS-CoV-2 discharged into the sewerage network. Moving upwards the numbers shrink, since not everybody with an infection is symptomatic, and not every symptomatic individual gets tested and there may be some delay or loss of reporting the local test data to national public health agencies. Ascending further, the numbers shrink by the nature of COVID-19: only a fraction of the reported COVID-19 cases end up in hospital, IC or die as a result of the disease.

Figure 2

The concept of sewage surveillance of SARS-CoV-2.

Figure 3

Decay of the SARS-CoV-2 RNA concentration in raw wastewater, stored at 5 °C, as determined with the RT-qPCR for the N2 gene fragment (methods see Medema et al., 2020).

Figure 4

Summary of reported concentrations of SARS-CoV-2 in faecal samples by day (noting data from Xu et al., 2020 is reported in days from hospitalisation).

Figure 5

Lognormal distribution fitted to the load of faecal mass shed per person per day (left) and gamma distribution (solid line) fitted to reported concentrations (dots – data from Figure 1) of RNA in faeces from reviewed studies.

Figure 6

Modelled relationship (Median (solid line), 5th and 95th quantiles) between the number of infected people in the population and concentration of RNA in sewage.

Figure 7

Comparison of sewage surveillance data and prevalence data for Amsterdam, The Netherlands, from Mar 1 to Jul 8, 2020. Load of SARS-CoV-2 RNA (N2 gene assay) in wastewater at the inlet of the Amsterdam WWTP (orange line and points; methods see Medema et al., 2020). Prevalence of laboratory-confirmed COVID-19 cases (blue points, data: National Institute of Public Health and the Environment, Netherlands), with 7d moving average (blue line) and of COVID-19 hospitalizations (grey points, data: National Institute of Public Health and the Environment, Netherlands), with 7d moving average (grey line).