What Does Sewage Reveal About Public Health?
Written by Nancy Selwood-Metcalfe
Edited by Isabel Louie
Surveilling sewage systems is an epidemiological approach for monitoring pathogen occurrence (1). It has emerged as a powerful tool in public health, offering the ability to detect pathogens at a community level before clinical cases are reported (2). Human pathogens can be detected in sewage because they are excreted through various bodily fluids, skin cells, and hair during infection, which then enter wastewater systems through everyday activities such as toilet use, bathing, and hand washing (1). Therefore, sewage systems act as a connection network, gathering microbial traces from across a community into a single source to reflect the population’s overall health status (1). This concept isn’t new, and there is evidence that this surveillance can act as an early warning system for infectious agents, including potential biothreats, by capturing pathogen shedding into wastewater before large outbreaks occur (1). Sewage provides a unique window into the health of populations, revealing information about infectious diseases, antimicrobial resistance, lifestyle-related health markers, and emerging public health threats (1,2,3). 
Photo by Julia Leavitt (jal569@cornell.edu), taken at Cornell University.
Wastewater surveillance has been used to monitor different infectious diseases in efforts to eradicate them globally, and has recently proved useful in tracking COVID-19 (2,4). In Hong Kong, routine sewage monitoring detected a high viral load of SARS-CoV-2 in a residential area with low infection rates and no recorded outbreaks (2). This was found three days before an infected individual was clinically confirmed (2). By using advanced allele-specific RT-qPCR methods, public health authorities were able to trace the source of the viral signal down to a building, perform targeted sampling, and issue compulsory testing orders (2). This rapid response helped prevent a potential outbreak and illustrated how wastewater surveillance can provide early warnings, guide rapid responses, and enable communities to act proactively against infectious threats, even in largely contained outbreaks (2,4). Beyond COVID-19, similar approaches have been used to detect pathogens such as poliovirus, further demonstrating that wastewater monitoring is a powerful, adaptable tool for tracking a wide range of infectious diseases (2,4).
Sewage monitoring not only detects pathogens but also provides valuable insights into antimicrobial resistance across communities– a growing global threat (3). Existing surveillance systems in hospitals and health care settings often miss resistant bacteria that have been circulating in wider populations (3). Sewage monitoring analysis, however, allows scientists to identify and quantify thousands of resistance genes in community sewage, offering a live picture of antimicrobial prevalence and trends (3). Because most antibiotic use occurs outside hospital settings and away from conventional surveillance, sewage monitoring can find resistance patterns that are usually overlooked, including seasonal fluctuations and emerging resistant strains (3). As this data provides both geographic and demographic material, it can support public health decision-making, guide antibiotic policies, and help detect emerging threats before they spread widely (3).
Photo by Julia Leavitt (jal569@cornell.edu).
In addition to pathogen surveillance, sewage monitoring can serve as epidemiological reflections of population-level behaviours and exposures (1). Advanced mass spectrometry techniques can be used to detect biomarkers of alcohol and nicotine consumption (such as ethyl sulphate and cotinine) in wastewater. Illicit drug metabolites can also be identified, which can be used to monitor illegal drug activity in communities (5). A study done in three U.S. cities correctly estimated the per-capita alcohol and cigarette use from sewage data, showing that wastewater-based epidemiology can accurately reflect population lifestyle patterns while remaining anonymous, cost-effective, and responsive to changes over time (5). Beyond behavioural markers, wastewater can also reflect environmental exposures to elements such as heavy metals and metalloids, which are harmful due to their toxic, genotoxic, and carcinogenic effects (6). Wastewater analysis therefore offers an alternative to traditional biomonitoring methods that are often invasive, expensive, and limited. Wastewater analysis is non-invasive and incorporates wider populations to track metal exposure and its health implications (6).
However, there are limitations to sewage surveillance. Although it allows for real-time insights into population behaviours without relying on self-reporting, we cannot identify individual cases, which restricts the precision of interventions (1,5). Sampling reliability can also vary due to uneven pathogen shedding, dilution, and sewer flow dynamics. Molecular methods, such as PCR, can even be hindered by interfering substances in wastewater, and cannot always distinguish between viable and nonviable organisms (1). This approach must therefore be balanced to account for ethical privacy considerations and the responsible interpretation of public data (1).
Despite its limitations, this ability to detect pathogens prior to outbreaks occurring remains invaluable as it enables early warning of both natural epidemics and potential bioterrorist events, allowing authorities to implement interventions quickly and prevent widespread transmission (1,2). Sewage surveillance also provides comprehensive, population-level data on antimicrobial resistance, disease prevalence, and lifestyle patterns, offering real-time and cost-effective insights into community health (1).
Nancy Selwood-Metcalfe 27’ is a Biological Sciences major in the College of Agriculture and life sciences, on exchange from London for the year. She can be reached at ns2233@cornell.edu.
Sources
(1) Sinclair RG, Choi CY, Riley MR, Gerba CP. Pathogen surveillance through monitoring of sewer systems. Advances in applied microbiology. 2008 Nov 20;65:249.
(2) Deng Y, Xu X, Zheng X, Ding J, Li S, Chui HK, Wong TK, Poon LL, Zhang T. Use of sewage surveillance for COVID-19 to guide public health response: A case study in Hong Kong. Science of the Total Environment. 2022 May 15;821:153250.
(3) Aarestrup FM, Woolhouse ME. Using sewage for surveillance of antimicrobial resistance. Science. 2020 Feb 7;367(6478):630-2.
(4) Deng Y, Zheng X, Xu X, Chui HK, Lai WK, Li S, Tun HM, Poon LL, Ding J, Peiris M, Leung GM. Use of sewage surveillance for COVID-19: a large-scale evidence-based program in Hong Kong. Environmental health perspectives. 2022 May 12;130(5):057008.
(5) Chen J, Venkatesan AK, Halden RU. Alcohol and nicotine consumption trends in three US communities determined by wastewater-based epidemiology. Science of the Total Environment. 2019 Mar 15;656:174-83.
(6) Markosian C, Mirzoyan N. Wastewater-based epidemiology as a novel assessment approach for population-level metal exposure. Science of the Total Environment. 2019 Nov 1;689:1125-32.
