# Wastewater-based epidemiology
Wastewater-based epidemiology (WBE) measures biomarkers, pathogens, or drug residues in community sewage to infer population-level trends in disease, substance use, or exposure. Because a sewer sample pools waste from everyone connected to a sewershed (population area draining into one sewer system), it yields aggregate community data rather than individual cases, and interpretation must account for variable shedding and pathogen stability.[1](https://www.ncbi.nlm.nih.gov/books/NBK591714/) The approach was used for decades in environmental surveillance of polioviruses and, before the COVID-19 pandemic, was applied mainly to chemicals including drugs of abuse, tobacco, and alcohol.[2](https://www.ecdc.europa.eu/sites/default/files/documents/wastewater-based-surveillance-framework.pdf) • [3](https://journals.asm.org/doi/10.1128/cmr.00103-22) After the first report of SARS-CoV-2 RNA in wastewater in March 2020, it became a mainstay complement to clinical surveillance.[4](https://wwwnc.cdc.gov/eid/article/27/9/pdfs/21-0753.pdf)
| Key fact | Value |
|---|---|
| What a sample reports | Pathogen gene copies per liter; flow-normalized loads (gene copies/day); per-capita mass loads of chemicals[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC8195746/) • [4](https://wwwnc.cdc.gov/eid/article/27/9/pdfs/21-0753.pdf) |
| Detection limit (SARS-CoV-2) | About 100 genome copies per liter; one infected person detectable among up to \( 4 \times 10^{5} \) people under ideal conditions[6](https://www.frontiersin.org/journals/virology/articles/10.3389/fviro.2021.776998/full) • [5](https://pmc.ncbi.nlm.nih.gov/articles/PMC8195746/) |
| Lead time over clinical data | 2 to 12 days before hospital admissions; median 6 days before reported cases[7](https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0313927) • [8](https://jehsd.ssu.ac.ir/article-1-1004-en.pdf) |
| Sampling standard | 24-hour composite samples strongly preferred; grab samples correlated with case rates at \( r = 0.398 \) versus \( r = 0.962 \) for composites[9](https://www.rki.de/EN/Topics/Research-and-data/Surveillance-panel/Wastewater-surveillance/Guideline.pdf?__blob=publicationFile&v=8) • [6](https://www.frontiersin.org/journals/virology/articles/10.3389/fviro.2021.776998/full) |
| Deployment scale | CDC NWSS exceeded 1,250 sites covering over 133 million people by October 2022; infrastructure existed in 58 countries[1](https://www.ncbi.nlm.nih.gov/books/NBK591714/) • [10](https://iwaponline.com/jwh/article/20/9/1284/90176/Research-needs-for-optimising-wastewater-based) |
| Legal mandate (EU) | Urban Wastewater Treatment Directive Article 17, in force 1 January 2025, requires surveillance for infectious disease and antimicrobial resistance[2](https://www.ecdc.europa.eu/sites/default/files/documents/wastewater-based-surveillance-framework.pdf) |
## How it works
The method rests on a mass balance. Raising 10 to the power of a treatment plant's influent concentration W (in Log\(_{10}\) gene copies per liter) and multiplying by the daily influent flow F (L/day) gives the number of gene copies of the analyte excreted by the community per day. After converting concentration and shedding to linear gene-copy quantities, dividing the daily analyte load (W in gene copies per liter multiplied by the daily influent flow F) by the product of I in gene copies per gram of feces and the per-capita fecal mass G (128 g feces per person per day in one implementation) yields the estimated number or fraction of infected people, which is compared against the census population of the sewershed.[11](https://www.nature.com/articles/s41598-022-21354-6) In a 53-week [Gainesville, Florida](https://www.edgepedia.org/gainesville-florida) study, this equation estimated COVID-19 prevalence with a median absolute error of 1.28% against a clinical reference group. The same mass balance was originally derived to estimate community illicit drug use from drug concentrations, individual excretion rates, and per-capita flow.[11](https://www.nature.com/articles/s41598-022-21354-6)
Normalization is the central unresolved choice. Concentrations can be converted to fluxes with flow data (gene copies per day, or mg/day for chemicals), which can be summed across adjacent sewersheds, or adjusted with fecal-strength markers such as pepper mild mottle virus (PMMoV) or crAssphage; the EU's 2021 recommendation endorsed normalization by population served and flow, with PMMoV or crAssphage as additional controls.[12](https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32021H0472) • [3](https://journals.asm.org/doi/10.1128/cmr.00103-22) A review of 247 articles found substantial variability in marker selection and reporting, often without clear explanation.[13](https://pubs.rsc.org/en/content/articlelanding/2026/ew/d5ew01049g) There is no agreement on which normalization yields the strongest correlations and earliest indication, and Germany's AMELAG program discontinued flow-rate normalization for [SARS-CoV-2](https://www.edgepedia.org/sars-cov-2) on 1 August 2025 after long-term analysis showed it did not improve data quality.[14](https://www.mdpi.com/2073-4441/16/9/1220) • [9](https://www.rki.de/EN/Topics/Research-and-data/Surveillance-panel/Wastewater-surveillance/Guideline.pdf?__blob=publicationFile&v=8)
## How it is done
The workflow has five steps: sampling, concentration, RNA or [DNA extraction](https://www.edgepedia.org/dna-extraction), quantification by (RT-)qPCR or qPCR, and reporting.[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC8195746/) Sampling uses untreated influent or primary sludge, collected as grab samples or 24-hour composites; composites smooth the diurnal variability that makes grab samples the least representative option.[15](https://aphl.org/docs/default-source/technical/eh-2022-sarscov2-wastewater-surveillance-testing-guide.pdf?sfvrsn=8a95cf1e_1) • [3](https://journals.asm.org/doi/10.1128/cmr.00103-22) AMELAG requires twice-weekly 24-hour composite samples taken by automatic sampler (grab samples not permitted), at least 3 L, cooled to 5 ± 3 °C.[9](https://www.rki.de/EN/Topics/Research-and-data/Surveillance-panel/Wastewater-surveillance/Guideline.pdf?__blob=publicationFile&v=8)
**Concentration and quantification.** Three main concentration families are used: polyethylene glycol (PEG) precipitation, pressure or [vacuum filtration](https://www.edgepedia.org/vacuum-filtration) onto charged membranes (0.1–0.45 µm), and centrifugal ultrafiltration; magnetic affinity particles perform comparably or better than membrane filtration, and automated paramagnetic bead extraction outperformed the column method tested.[9](https://www.rki.de/EN/Topics/Research-and-data/Surveillance-panel/Wastewater-surveillance/Guideline.pdf?__blob=publicationFile&v=8) • [16](https://pubs.rsc.org/en/content/articlehtml/2024/ew/d3ew00958k) PCR is susceptible to inhibitors such as humic and fulvic acids; ultrafiltration is reported as the most effective inhibitor-removal method among those compared.[14](https://www.mdpi.com/2073-4441/16/9/1220) [Digital PCR](https://www.edgepedia.org/digital-pcr) has a lower limit of detection and is 2 to 5 times more sensitive than qPCR, though side-by-side method pairs differed on average by a factor of 3.6 in measured levels.[17](https://www.mdpi.com/2076-2607/13/5/1169) • [16](https://pubs.rsc.org/en/content/articlehtml/2024/ew/d3ew00958k) Results are reported as genomic copies per liter, with documented limits of detection and quantification.[9](https://www.rki.de/EN/Topics/Research-and-data/Surveillance-panel/Wastewater-surveillance/Guideline.pdf?__blob=publicationFile&v=8)
## Origin
Detecting pathogens in sewage long predates molecular methods. [John R. Paul](https://www.edgepedia.org/john-r-paul), James D. Trask, and C. S. Culotta reported poliomyelitic virus in sewage in *Science* in 1939.[18](https://doi.org/10.1126/science.90.2333.258) Yale scientists Paul and Trask hypothesized that poliovirus from infected feces might be present in sewage, and in the 1960s [Joseph Melnick](https://www.edgepedia.org/joseph-l-melnick) at [Baylor College of Medicine](https://www.edgepedia.org/baylor-college-of-medicine) monitored polio in Houston's wastewater; observing a rise in the virus, he convinced authorities to advance the oral polio vaccine, the first significant public health action based on viral wastewater analysis.[19](https://www.annualreviews.org/content/journals/10.1146/annurev-med-062024-125121) Earlier precedents include tracing rectal bilharziasis to wastewater contaminating a reservoir in 1954 and a 1980 WHO report on cholera surveillance in water bodies as an early-warning platform.[20](https://pmc.ncbi.nlm.nih.gov/articles/PMC8499728/)
The modern chemical era began with a primarily theoretical proposal to monitor illicit drug use through sewage; cocaine was successfully extracted and quantified from wastewater four years later, initially at detection limits above 50 ng/L.[21](https://jeas.springeropen.com/counter/pdf/10.1186/s44147-023-00180-1.pdf) • [17](https://www.mdpi.com/2076-2607/13/5/1169) SARS-CoV-2 transformed the field: RNA was first detected in wastewater in March 2020, and a 2020 study by Jordan Peccia and colleagues in *Nature Biotechnology* showed that wastewater SARS-CoV-2 RNA measurements track community infection dynamics.[4](https://wwwnc.cdc.gov/eid/article/27/9/pdfs/21-0753.pdf) • [22](https://doi.org/10.1038/s41587-020-0684-z)
## Variants
A terminology review recommends "wastewater-based epidemiology" for the science of relating microbes or chemicals in wastewater to public health, "wastewater surveillance" for continuous monitoring of health outcomes, and "environmental surveillance" for the long-standing poliovirus programs.[20](https://pmc.ncbi.nlm.nih.gov/articles/PMC8499728/) • [2](https://www.ecdc.europa.eu/sites/default/files/documents/wastewater-based-surveillance-framework.pdf) Major platforms include the US CDC National Wastewater Surveillance System (NWSS), launched with HHS in September 2020;[1](https://www.ncbi.nlm.nih.gov/books/NBK591714/) the EU Recommendation of 17 March 2021, which required national SARS-CoV-2 systems by 1 October 2021 covering cities over 150,000 inhabitants with at least two samples per week;[12](https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32021H0472) Germany's AMELAG, in which RKI and UBA monitor SARS-CoV-2, influenza viruses, and RSV nationwide;[9](https://www.rki.de/EN/Topics/Research-and-data/Surveillance-panel/Wastewater-surveillance/Guideline.pdf?__blob=publicationFile&v=8) WastewaterSCAN, about 12% of NWSS sites, monitoring 10 additional targets including influenza, RSV, norovirus GIII, mpox, *Candida auris*, and hepatitis A;[23](https://www.ncbi.nlm.nih.gov/books/NBK610722/) and Texas's TexWEB, which uses near-real-time sequencing instead of PCR and has tracked nearly 500 viruses across 15 cities covering about 25% of the state's population.[19](https://www.annualreviews.org/content/journals/10.1146/annurev-med-062024-125121)
**Variant tracking from sewage.** Smruthi Karthikeyan and colleagues reported in *Nature* in 2022 the Freyja deconvolution software, which resolves multiple virus strains from mixed wastewater samples; with only 2.6% as many sequenced wastewater samples as clinical samples, Alpha and Delta were detected up to 14 days before first clinical genomic detection, and Omicron was seen at just over 1% abundance 11 days early at a plant serving over 2 million residents.[24](https://doi.org/10.1038/s41586-022-05049-6) Standard lineage tools such as pangolin and UShER cannot estimate relative abundances in mixtures, since they were designed for clinical samples with a single dominant variant.[24](https://doi.org/10.1038/s41586-022-05049-6) The VaQuERo approach, which regresses marker mutations present in over 80% of a variant's GISAID genomes, agreed with case surveillance at Kendall \( \tau = 0.43 \).[25](https://link.springer.com/article/10.1038/s41587-022-01387-y)
## Applications
Beyond COVID-19 dashboards, the longest-standing application is polio: during global eradication, wastewater surveillance assessed polio circulation and immunization efficacy, and Israel's long-standing program contributed to a swift response during the 2013 poliovirus reemergence, enabling targeted vaccination.[26](https://journals.plos.org/globalpublichealth/article?id=10.1371%2Fjournal.pgph.0000061) • [19](https://www.annualreviews.org/content/journals/10.1146/annurev-med-062024-125121) During the 2022 mpox outbreak, the Netherlands, the United States, Brazil, and Spain began testing wastewater for mpox virus DNA, with results indicating community transmission before clinical case numbers climbed; avian influenza detection in wastewater, likely from dairy cow inputs, may signal zoonotic transmission.[19](https://www.annualreviews.org/content/journals/10.1146/annurev-med-062024-125121) • [2](https://www.ecdc.europa.eu/sites/default/files/documents/wastewater-based-surveillance-framework.pdf) A meta-analysis reported wastewater positivity of 62% for influenza A and 36% for influenza B in 2022–2023, alongside RSV, norovirus, and polio detections.[8](https://jehsd.ssu.ac.ir/article-1-1004-en.pdf)
Wastewater signals have triggered actions: an elevated signal in Guadalupe, Arizona, beginning the week of 11 May 2020 prompted interventions including face-mask mandates,[27](https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247%2822%2900289-0/fulltext) and Arizona's WATERS program used a "Levels of Concern" metric based on SARS-CoV-2 concentrations to trigger responses within 24-hour sample processing.[28](https://www.frontiersin.org/journals/public-health/articles/10.3389/fpubh.2024.1418681/full) In Denmark, integrating wastewater data with clinical hospitalization data improved COVID-19 hospitalization forecasts.[2](https://www.ecdc.europa.eu/sites/default/files/documents/wastewater-based-surveillance-framework.pdf)
## Limitations and alternatives
**Sensitivity and lead time vary.** Pooled SARS-CoV-2 positivity across 29 studies was 59.5%, highest in sludge (98.8%) and lower in hospital wastewater (33.1%); wastewater preceded reported cases by a median of 6 days (IQR 2–19.5) and US hospital admissions by 2 to 12 days.[8](https://jehsd.ssu.ac.ir/article-1-1004-en.pdf) • [7](https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0313927)
**Failure modes.** Rain and stormwater dilute the signal; graywater is a major dilutive factor; temperatures above 25 °C and saline conditions increase RNA decay; and industrial discharges, sewer length, and population fluctuations (for example tourism) add noise.[26](https://journals.plos.org/globalpublichealth/article?id=10.1371%2Fjournal.pgph.0000061) • [14](https://www.mdpi.com/2073-4441/16/9/1220) • [29](https://link.springer.com/article/10.1007/s12560-023-09573-0) In the US, 20% of households lack municipal sewage collection and are absent from the data.[26](https://journals.plos.org/globalpublichealth/article?id=10.1371%2Fjournal.pgph.0000061) Smaller plants show significantly greater variability, and correlations with clinical data are watershed-specific: in a 2-year Italian study the wastewater–clinical alignment disappeared as infection became endemic and most cases were asymptomatic, and in [Tempe, Arizona](https://www.edgepedia.org/tempe-arizona), wastewater no longer led clinical data once testing capacity improved.[7](https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0313927) • [29](https://link.springer.com/article/10.1007/s12560-023-09573-0) • [27](https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247%2822%2900289-0/fulltext) Different laboratories and methods can produce concentration differences greater than an order of magnitude, and one meta-analysis found only 26% of studies reported qPCR quality-control details meeting minimum criteria.[3](https://journals.asm.org/doi/10.1128/cmr.00103-22) • [10](https://iwaponline.com/jwh/article/20/9/1284/90176/Research-needs-for-optimising-wastewater-based)
**Compared with clinical reporting**, wastewater returns results in about 5 to 7 days versus 2 weeks for clinical case counts in one program, samples the whole sewershed regardless of testing-seeking behavior, and delivers population-level rather than individual data; it is more variable than clinical data and should not be the sole basis for decisions.[30](https://www.cdc.gov/advanced-molecular-detection/media/pdfs/ToolkitModule_2.7-508C.pdf) • [2](https://www.ecdc.europa.eu/sites/default/files/documents/wastewater-based-surveillance-framework.pdf) • [26](https://journals.plos.org/globalpublichealth/article?id=10.1371%2Fjournal.pgph.0000061) Since late 2023, the EU Directive's Article 17 took effect on 1 January 2025 with AMR implementing acts due by July 2026, NWSS added mpox and piloted influenza A/B and RSV, and AMELAG adopted generalized additive model smoothing for trend calculation, while standardized reporting guidelines remain a stated need.[2](https://www.ecdc.europa.eu/sites/default/files/documents/wastewater-based-surveillance-framework.pdf) • [23](https://www.ncbi.nlm.nih.gov/books/NBK610722/) • [9](https://www.rki.de/EN/Topics/Research-and-data/Surveillance-panel/Wastewater-surveillance/Guideline.pdf?__blob=publicationFile&v=8) • [13](https://pubs.rsc.org/en/content/articlelanding/2026/ew/d5ew01049g)
## References
1. [Introduction - Wastewater-based Disease Surveillance for Public Health Action (National Academies)](https://www.ncbi.nlm.nih.gov/books/NBK591714/)
2. [ECDC framework to guide the integration of wastewater-based surveillance into infectious disease surveillance at the EU/EEA level](https://www.ecdc.europa.eu/sites/default/files/documents/wastewater-based-surveillance-framework.pdf)
3. [Wastewater-based surveillance as a tool for public health action: SARS-CoV-2 and beyond](https://journals.asm.org/doi/10.1128/cmr.00103-22)
4. [Wastewater Surveillance for SARS-CoV-2: Using It to Support Public Health Decision-Making (Emerging Infectious Diseases)](https://wwwnc.cdc.gov/eid/article/27/9/pdfs/21-0753.pdf)
5. [Technical framework for wastewater-based epidemiology of SARS-CoV-2](https://pmc.ncbi.nlm.nih.gov/articles/PMC8195746/)
6. [Reliability of Wastewater Analysis for Monitoring COVID-19 Incidence Revealed by a Long-Term Follow-Up Study](https://www.frontiersin.org/journals/virology/articles/10.3389/fviro.2021.776998/full)
7. [SARS-CoV-2 surveillance in US wastewater: Leading indicators and data variability analysis in 2023–2024](https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0313927)
8. [Wastewater-Based Epidemiology for Infectious Disease Surveillance: A Systematic Review and Meta-Analysis Focused on SARS-CoV-2](https://jehsd.ssu.ac.ir/article-1-1004-en.pdf)
9. [Wastewater Monitoring for Epidemiological Situation Assessment: AMELAG Technical guide for wastewater surveillance (Status: 11.2025)](https://www.rki.de/EN/Topics/Research-and-data/Surveillance-panel/Wastewater-surveillance/Guideline.pdf?__blob=publicationFile&v=8)
10. [Research needs for optimising wastewater-based epidemiology monitoring for public health protection](https://iwaponline.com/jwh/article/20/9/1284/90176/Research-needs-for-optimising-wastewater-based)
11. [Assessment of a mass balance equation for estimating community-level prevalence of COVID-19 using wastewater-based epidemiology in a mid-sized city](https://www.nature.com/articles/s41598-022-21354-6)
12. [Commission Recommendation (EU) 2021/472 of 17 March 2021 on a common approach to establish a systematic surveillance of SARS-CoV-2 and its variants in wastewaters in the EU](https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32021H0472)
13. [Assessing normalization methods in wastewater based epidemiology: a systematic review (Environmental Science: Water Research & Technology)](https://pubs.rsc.org/en/content/articlelanding/2026/ew/d5ew01049g)
14. [Precision and Accuracy Limits of Wastewater-Based Epidemiology, Lessons Learned from SARS-CoV-2: A Scoping Review](https://www.mdpi.com/2073-4441/16/9/1220)
15. [SARS-CoV-2 Wastewater Surveillance Testing Guide for Public Health Laboratories](https://aphl.org/docs/default-source/technical/eh-2022-sarscov2-wastewater-surveillance-testing-guide.pdf?sfvrsn=8a95cf1e_1)
16. [Wastewater-based protocols for SARS-CoV-2: insights into virus concentration, extraction, and quantitation methods from two years of public health surveillance](https://pubs.rsc.org/en/content/articlehtml/2024/ew/d3ew00958k)
17. [Advances in Wastewater-Based Epidemiology for Pandemic Surveillance: Methodological Frameworks and Future Perspectives (Microorganisms)](https://www.mdpi.com/2076-2607/13/5/1169)
18. [John R. Paul, James D. Trask, C. S. Culotta (1939). Poliomyelitic Virus in Sewage. Science.](https://doi.org/10.1126/science.90.2333.258)
19. [Sewers to Solutions: A Guide to Wastewater Pathogen Monitoring](https://www.annualreviews.org/content/journals/10.1146/annurev-med-062024-125121)
20. [Wastewater monitoring, surveillance and epidemiology: a review of terminology for a common understanding](https://pmc.ncbi.nlm.nih.gov/articles/PMC8499728/)
21. [Optimization of sewage sampling for wastewater-based epidemiology through stochastic modeling](https://jeas.springeropen.com/counter/pdf/10.1186/s44147-023-00180-1.pdf)
22. [Jordan Peccia and colleagues (2020). Measurement of SARS-CoV-2 RNA in wastewater tracks community infection dynamics. Nature Biotechnology.](https://doi.org/10.1038/s41587-020-0684-z)
23. [Potential Target Expansion for National Endemic Disease Surveillance - Wastewater-based Disease Surveillance for Public Health Action (NASEM)](https://www.ncbi.nlm.nih.gov/books/NBK610722/)
24. [Smruthi Karthikeyan and colleagues (2022). Wastewater sequencing reveals early cryptic SARS-CoV-2 variant transmission. Nature.](https://doi.org/10.1038/s41586-022-05049-6)
25. [Viral variant-resolved wastewater surveillance of SARS-CoV-2 at national scale (Nature Biotechnology)](https://link.springer.com/article/10.1038/s41587-022-01387-y)
26. [Wastewater network infrastructure in public health: Applications and learnings from the COVID-19 pandemic](https://journals.plos.org/globalpublichealth/article?id=10.1371%2Fjournal.pgph.0000061)
27. [Leveraging an established neighbourhood-level, open access wastewater monitoring network to address public health priorities: a population-based study](https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247%2822%2900289-0/fulltext)
28. [A framework for integrating wastewater-based epidemiology and public health (Frontiers in Public Health)](https://www.frontiersin.org/journals/public-health/articles/10.3389/fpubh.2024.1418681/full)
29. [Critical Needs for Integrated Surveillance: Wastewater-Based and Clinical Epidemiology in Evolving Scenarios with Lessons Learned from SARS-CoV-2](https://link.springer.com/article/10.1007/s12560-023-09573-0)
30. [Module 2.7: Wastewater-based variant tracking for SARS-CoV-2 (CDC COVID-19 Genomic Epidemiology Toolkit)](https://www.cdc.gov/advanced-molecular-detection/media/pdfs/ToolkitModule_2.7-508C.pdf)
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*Topic: Encyclopedia › Life and health › Human health and medicine › Public health and healthcare › Disease surveillance and pandemic preparedness*
*Initially written Sep 29, 2026 · Reviewed: Sep 30, 2026 · Edited: Sep 30, 2026 · Last review: Sep 30, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license