Wastewater surveillance or detection is the practice of monitoring sewage in specific cities or other regions and using the prevalence of specific pathogens in the wastewater to estimate incidence or prevalence of the disease in the population linked to that wastewater. For years, the primary pathogen tracked in most wastewater surveillance has been poliovirus, but that has been expanding since the COVID-19 pandemic. More pathogens, including SARS-CoV-2, are now included in wastewater surveillance.
Other uses of wastewater surveillance include estimating use of prescription drugs, illicit drugs, pesticides, household cleaners, or other non-pathogen chemicals. For example, the U.S. Government Accountability Office has noted that Australia uses wastewater surveillance of illicit drugs to determine the effectiveness of law enforcement drug seizures.
Deeper dive
This article does a good job of describing how wastewater surveillance works. One important point to know is that there are multiple methods that can be used, particularly in terms of whether the sampling occurs in smaller, localized areas or in larger community-wide sewage. For example, sampling from a single manhole near a particular school can provide very precise information about infections at that school whereas a city sewage provides information about the larger metro area. According to the CDC’s Morbidity and Mortality Weekly Report, as of December 2023, there were 53 jurisdictions across the U.S. using wastewater surveillance for infectious diseases.
Although most pathogens surveilled in wastewater are shed in human feces, there are other ways pathogens can make their way to sewage, such as other bodily fluid secretions, skin and hair, and clothing from laundering. For example, insect-borne encephalitis viruses can be detected in urine. Pathogens commonly included in many current wastewater surveillance programs include poliovirus, SARS-CoV-2, enterovirus D68, influenza, and respiratory syncytial virus (RSV), but there are other pathogens that could be incorporated into more robust wastewater surveillance programs.
Some things to keep in mind when considering wastewater surveillance:
Different pathogens persist for different durations. The period of time that poliovirus can remain detectable in wastewater may differ from the period of time that SARS-CoV-2 can remain detectable. Knowing a pathogen’s duration of detection is important for making estimates about current or recent-past cases.
Different pathogens can be shed by people at different rates. Not everyone infected with a particular pathogen may necessarily shed it as easily or in as high a concentration as another pathogen.
People can shed a pathogen without being symptomatic. In some ways, wastewater surveillance can provide a more accurate sense of the current prevalence of a condition than medical case prevalence can. However, in other ways, wastewater surveillance can overestimate prevalence since not everyone with an infection who is shedding a pathogen is necessarily symptomatic or contagious to others. In fact, some people can shed a pathogen without even being infected if they were simply exposed to it but it never colonized in their body.
Wastewater data can be particularly useful as an early warning signal for disease outbreaks or an uptick in endemic diseases, but the data needs to be standardized to be used.