While COVID-19 has revealed much about the health of our country including America's established racial and socioeconomic inequities in population health, the decline in federal funding of public health, neglected public health infrastructure, etc, it has also provided an opportunity for innovation and scientific advancement. Much of the innovation has focused on the development of new vaccines and treatments as well as creating models to predict how COVID-19 will spread in populations. However, efforts have also been made to support COVID-19 surveillance, providing an important source of information to guide decision making by public health officials. COVID-19 testing has been the primary source of surveillance data, peaking at nearly 1.8 million tests per day in November 2020 to January 2021, dropping to more than 500 000 tests per day in July 2021, and increasing again to 1.5 million tests per day in December 2021.1 Relying on testing alone provides only a partial picture of COVID-19 in a community since many people infected with SARS-CoV-2 are asymptomatic or presymptomatic and do not present for testing. A relatively small network of scientists aimed to fill this gap early in the pandemic by testing wastewater for SARS-CoV-2.2 This work has expanded since 2020, and wastewater surveillance for SARS-CoV-2 is taking place all over the world in communities and on university campuses. For example, researchers in Argentina monitored a large metropolitan population of 1.2 million residents from July 2020 to January 2021 by testing wastewater at 2 treatment plants and were able to monitor the virus during its rise, growth, peak, and fall for 26 weeks.3 The authors' results also demonstrated a positive correlation between SARS-CoV-2 viral load and diagnosed COVID-19 cases per week, indicating that wastewater surveillance can be a powerful indicator of population health.

Detecting pathogens in wastewater has been in practice for some time. In the 1930s and 1940s, researchers turned to wastewater to detect the virus causing poliomyelitis to confirm the hypothesis that the virus was spread via the fecal-oral route.4 More recently in May 2013, polio was detected in sewage in a community in Israel and, by October 2013, wild poliovirus was detected in 140 wastewater specimens from 25 sites throughout the country despite no cases of paralysis.5 This startling discovery led Israel to reconsider its use of the inactivated polio vaccine (IPV), for which Israel has a high vaccination rate of more than 95%. IPV replaced the oral live-virus vaccine (OPV) in Israel, which not only protects against paralysis but also blocks transmission of the virus. However, the weakened live virus in the OPV vaccine can cause paralysis in rare instances. In October 2013, the Israeli government opted to reintroduce OPV with IPV into the standard immunization schedule to address the "silent" polio epidemic. Wastewater has also been used to detect norovirus. Researchers in Sweden detected large amounts of norovirus in wastewater 2 to 3 weeks before most cases were identified, illustrating the capability of wastewater surveillance to provide early warning before cases are identified by the health care system.6

Testing wastewater to detect pathogens offers numerous advantages to traditional passive surveillance in which people are diagnosed with a disease. Waste-water surveillance is highly cost-effective-entire communities can be monitored with one sample, which can also provide genetic information. Wastewater surveillance can identify hot spots and vulnerable populations within a community (ie, microsewersheds), offer early detection of potential outbreaks, include little sampling bias since everyone served by municipal sewage collection systems participates, no testing fatigue, and capture people with symptomatic and asymptomatic infection. The US Centers for Disease Control and Prevention (CDC) appreciates the value of wastewater surveillance for COVID-19 and established the National Wastewater Surveillance System (NWSS).7 The CDC and the US Department of Health and Human Services, in collaboration with numerous federal agencies, initiated the NWSS to provide public health officials with data they need to better monitor the spread of SARS-CoV-2 in communities. Beyond COVID-19 virus, polio virus, and norovirus, many pathogens have been detected in feces and/or detected in wastewater including Campylobacter, Cryptosporidium, dengue viruses, Escherichia coli, hepatitis A virus, influenza, rotavirus, Salmonella, and Yellow Fever virus, offering numerous opportunities to detect and control outbreaks at an early stage.

The NWSS is an important step; however, given the distinct advantages and opportunities, we should integrate wastewater surveillance into existing communicable disease surveillance systems throughout the United States. Wastewater surveillance systems are akin to syndromic surveillance systems that are in wide use and offer similar advantages to passive surveillance systems-they do not rely on diagnoses and can provide early detection of outbreaks. Expanding wastewater surveillance into every US community will require a large financial commitment and should not come at the expense of existing surveillance systems as wastewater surveillance is not a stand-alone system and complements other surveillance systems. However, additional work is needed to address challenges of wastewater surveillance before large investments are made. First, turnaround times from sample collection to testing need to be shortened to maximize the usefulness of the results. Turnaround times can be particularly challenging when a central laboratory is processing and testing samples from a large coverage area (eg statewide). Second, methods need to be standardized across laboratories to facilitate interpretation of results across locations. Third, there are some questions regarding the sensitivity of the analytical testing for SARS-CoV-2 as well as other pathogens in low-prevalence settings. That is, what is the total number of cases required for detection in wastewater? Regardless of the pathogen, the sensitivity of testing needs to be sufficiently low to increase the usefulness of results by public health officials. Finally, as users of the data, public health officials need to be engaged to determine the most effective way for results to be presented to, again, maximize usefulness and rapid interpretation. It is imperative that we develop this vital public health infrastructure to not only better respond to known communicable disease threats but also position ourselves to respond to future threats more quickly.

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