Wastewater surveillance is a method of testing waste (sewage) for pathogens of interest to public health. It’s unique in that it is time-based and brings together a wide area’s pathogens to a central location1.
The following pathogens have been detected in sewage1:
- SARS-CoV-1 Outbreak (2002-2004)
- Polio
- HIV
- Hepatitis B
SAR-CoV-2 and COVID-19 pandemic
Wastewater surveillance is and was particularly useful in the COVID-19 pandemic. During infection in humans, there is viral shedding of SARS-CoV-2 RNA in the feces2. This RNA then becomes detectable in wastewater either at the sewage treatment plant or further up stream (e.g. at hospital level, university, etc). Wastewater is seen as an earlier predictor of infections since it captures a wide area and asymptomatic cases3. However, this has been challenged since the RNA load is not predictable across infections and may just be due to reporting lags4.
How does it work?
Samples are collected at a catchment point, typically un-treated sewer water (influent) entering a treatment plant. However, one study showed that SARS-CoV-2 is detectable in the sludge (first solids that settle during treatment)5. Typically 100ml to 200ml of waste water is collected6.
For influent studies, viral concentration processes are then applied7:
- treating with a glycine buffer
- filtration,
- skimmed milk flocculation
- polyethylene glycol (PEG) precipitation
RNA is then extracted from the sample and Reverse-transcription qPCR (RT-qPCR) is applied to identify SARS-CoV-26,7.
1. Sinclair, R. G., Choi, C. Y., Riley, M. R. & Gerba, C. P. Chapter 9 - Pathogen Surveillance Through Monitoring of Sewer Systems. in Advances in Applied Microbiology (eds. Laskin, A. I., Sariaslani, S. & Gadd, G. M.) vol. 65 249–269 (Academic Press, 2008).
2. Daughton, C. G. Wastewater surveillance for population-wide Covid-19: The present and future. Science of The Total Environment 736, 139631 (2020).
3. Randazzo, W. et al. SARS-CoV-2 RNA in wastewater anticipated COVID-19 occurrence in a low prevalence area. Water Research 181, 115942 (2020).
4. Bibby, K., Bivins, A., Wu, Z. & North, D. Making waves: Plausible lead time for wastewater based epidemiology as an early warning system for COVID-19. Water Research 202, 117438 (2021).
5. Kaplan, E. H., Zulli, A., Sanchez, M. & Peccia, J. Scaling SARS-CoV-2 wastewater concentrations to population estimates of infection. Scientific Reports 12, 3487 (2022).
6. Peinado, B., Martínez-García, L., Martínez, F., Nozal, L. & Sánchez, M. B. Improved methods for the detection and quantification of SARS-CoV-2 RNA in wastewater. Scientific Reports 12, 7201 (2022).
7. Philo, S. E. et al. A comparison of SARS-CoV-2 wastewater concentration methods for environmental surveillance. The Science of the Total Environment 760, 144215 (2021).