Wastewater-based infectious disease surveillance systems detect and quantify the presence of pathogen biomarkers, most commonly microbial deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), that are shed by persons into a municipal sewer system. Whereas clinical laboratory testing tracks individual cases of infection, sampling and analysis at the wastewater treatment plant level (termed community-level wastewater surveillance) provides aggregate data from the homes, businesses, and other institutions that share a common sewer system. Wastewater surveillance was used effectively prior to the COVID-19 pandemic, most notably as a tool to monitor and respond to poliovirus, but the pandemic led to widespread implementation of wastewater surveillance in communities across the United States. Early in the COVID-19 pandemic, several municipalities and universities developed wastewater surveillance systems to explore the feasibility and potential public health value of SARS-CoV-2 RNA detection in wastewater. In September 2020, the U.S. Centers for Disease Control and Prevention (CDC) launched the National Wastewater Surveillance System (NWSS) in partnership with the U.S. Department of Health and Human Services to respond to the need for centralization and coordination of and communication between these efforts.
At CDC’s request, the National Academies of Sciences, Engineering, and Medicine appointed a committee to review the current usefulness of community-level wastewater surveillance and its potential value for control and prevention of infectious diseases beyond the first 2 years of the COVID-19 pandemic. For the purpose of this study, community-level wastewater-based disease surveillance implies sampling at wastewater treat-
ment plants; these treatment plants serve communities across a wide range of scales from as few as 100 to as many as 4 million people, with a median community size of 45,000 people. The committee’s charge has two phases. In this report, which encompasses Phase 1, the committee was tasked to review how wastewater surveillance has been helpful to understand COVID-19 in communities and inform local public health decisions. The committee was also charged to examine the value of applications beyond the current COVID-19 pandemic, describe the characteristics of a robust national wastewater surveillance system, and discuss approaches to increase the public health impact of such a system (see Box 1-4 for the committee’s complete Phase 1 statement of task). The Phase 2 study will offer a detailed assessment of technical constraints and opportunities for the NWSS, including research and technology development needs.
Wastewater surveillance has proven to be a valuable component of the nation’s emergency response to the COVID-19 pandemic and will remain a critical data source for public health action in responding to COVID-19. Notably, as at-home testing increases and clinical laboratory testing and reporting decreases, wastewater surveillance for new variants and their spread will take on increasing importance. The pandemic spurred tremendous innovation and technological advances in wastewater surveillance, and ongoing knowledge development can help address gaps and improve analytical methods and data interpretation, not only for COVID-19 but also for newly emergent and re-emerging infectious diseases. Looking forward, the committee envisions a national wastewater surveillance system that is flexible, equitable, sustainable, integrated, and actionable, and recommends criteria and a process for adapting the NWSS to additional microbial threats. The committee also recommends approaches to address ethical and privacy concerns and develop a more representative wastewater surveillance system. Predictable and sustained federal funding as well as ongoing coordination and collaboration among many partners will be critical to the effectiveness of the NWSS moving forward. The committee’s conclusions and recommendations are discussed below.
WASTEWATER SURVEILLANCE FOR COVID-19
The experience with wastewater surveillance during COVID-19 demonstrates that these data are useful for informing public health action and that wastewater surveillance is worthy of further development and continued investment. Public health agencies that invested in collecting, analyzing, and interpreting the data found them useful to inform policy decisions (e.g., masking and social distancing rules), allocation of public health resources (e.g., testing and vaccination sites, public notification efforts), and allocation of clinical resources (e.g., staffing, hospital beds).
These data rarely stood alone but rather were frequently used in conjunction with other disease surveillance data sets (e.g., case and hospitalization counts), each with their own limitations and advantages, to decide on appropriate public health actions and resource allocations. Information on changing SARS-CoV-2 RNA levels in wastewater was shared with the public, often on dashboards, to help inform personal decision making. The launch of CDC’s NWSS created an expanded network of utilities and health departments monitoring SARS-CoV-2 in wastewater, thus strengthening COVID-19 surveillance capacity and providing support and guidance for sampling, analyzing, and interpreting data for public health action.
Wastewater surveillance data have been particularly useful for understanding SARS-CoV-2 trends and the spread of variants. Wastewater surveillance provides a method to passively assess trends in COVID-19 burden in a community unbiased by the availability of testing or test-seeking behavior. As COVID-19 clinical testing and reported case data became less reliable in recent months due to many factors, including increased at-home testing, wastewater surveillance provided continued information on where the virus was circulating and the degree of exposure risk. Although wastewater surveillance is not currently being used as a standalone method to reliably estimate the number of community infections, SARS-CoV-2 wastewater data have correlated with case data and other conventional public health surveillance data. Depending on a number of factors, including wastewater sampling frequency, the time required for sample transport and analysis, and the time required for data reporting, wastewater SARS-CoV-2 viral trends have the potential to be reported more quickly or along a more consistent time frame than conventional disease surveillance reporting. Wastewater surveillance also provides comprehensive information on the relative proportions of known variants, and genome sequencing of wastewater samples is an effective strategy to screen for emerging variants among a large contributing population, thus providing information in advance of clinical testing data.
The emergency response to the COVID-19 pandemic spurred innovation and rapid development and implementation of wastewater surveillance; the challenge is now to unify sampling design, analytical methods, and data interpretation to create a truly representative national system while maintaining continued innovation. Early challenges in initial surveillance sites focused on analytical capacity, sampling design, and data interpretation. The pandemic inspired innovation, which led to a diversity of approaches and methods rather than a single standard method. To date, sites within the NWSS have been based primarily on wastewater utility and public health jurisdiction willingness to participate, including volunteering time and resources, and thus do not comprise a representative national system. Importantly, participating sites have successfully built new partnerships
across professional communities with limited prior interactions, spurring innovation and increased efficiency. The challenge is to formalize these roles and partnerships and ensure national representation with best practices for collection, analysis, and use of the data.
VISION FOR A NATIONAL WASTEWATER SURVEILLANCE SYSTEM
Wastewater surveillance is and will continue to be a valuable component of the nation’s strategy to manage infectious disease outbreaks, including continued surveillance of SARS-CoV-2 variants, resurgences of known pathogens, and newly emergent pathogens. The emergency establishment of wastewater surveillance has proven its value, and the efforts at local and national scales to establish the NWSS provide a solid basis for expanded applications. Infectious diseases, whether endemic, seasonal, newly emergent, or re-emergent, are dynamic and never fully predictable. The high likelihood that SARS-CoV-2 variants will continue to emerge and circulate is alone a strong rationale to maintain and strengthen a national wastewater surveillance system. The recent use of wastewater surveillance for poliovirus and mpox in mid-2022 illustrates the advantages of a maintained national system for detecting re-emerging pathogens and pathogens recently introduced into the United States.
To achieve its goals, a national wastewater surveillance system should be flexible, equitable, integrated, actionable, and sustainable. Flexibility includes the ability to track multiple pathogens simultaneously and pivot quickly to new threats. A national wastewater surveillance system should be as equitable as possible across population demographics, with efforts to engage underrepresented communities and extrapolate findings, where feasible, to unsewered communities. Integration, including coordination and collaboration across multiple partners (e.g., utilities, laboratories, and public health agencies) and triangulation of data from different disease surveillance systems, ensures effective data interpretation in support of public health decision making. For the information to be actionable and inform decisions about clinical and public health resource allocations as well as policy decisions, it must also be timely, available, reliable, representative, and interpretable. Finally, the system needs to be fiscally and operationally sustainable. Although the NWSS supports both local and national public health decision making, a sustainable national wastewater surveillance program may not serve every locality’s objectives but should allow for locally funded initiatives, such as pilot surveillance of a pathogen of emerging regional concern.
When evaluating potential targets for future wastewater surveillance, CDC should consider three criteria: (1) public health significance of the threat, (2) analytical feasibility for wastewater surveillance, and (3) use
fulness of community-level wastewater surveillance data to inform public health action. Applying these criteria to known and emergent/re-emergent pathogens of concern can guide strategic allocation of effort and resources. Assessment of the public health significance of a microbial threat is important to develop and maintain a system that is responsive to current public health needs. Assessment of the feasibility to detect a specific pathogen in wastewater for disease surveillance is necessary to determine technical readiness and can also drive research or technology development for microbial threats that meet the other criteria. Finally, it is critical that the value of wastewater surveillance information for a given pathogen be considered in the context of the broader universe of surveillance approaches so as to maximize the use of resources to inform public health action (e.g., allocation of clinical or public health resources). Candidate pathogens will need to be re-evaluated periodically as scientific knowledge, technology, and infectious disease risks evolve.
Temporal and spatial resolution of the NWSS sampling program should be subject to intentional design, informed by rigorous and iterative analysis of data for prioritized pathogens. Collaborative and frequent analysis of incoming NWSS data is essential to determine the spatial and temporal scales of sampling and analysis needed, both for effective COVID-19 monitoring as well as detection of emerging pathogens. Temporal and spatial resolution should be regularly re-evaluated to ensure the system is capable of detecting meaningful change with sufficient lead time needed to inform public health action. CDC should also give careful attention to the need for more representative sampling for prioritized use cases. Currently, the system consists of localities, tribes, and states that were willing and able to participate during a pandemic emergency, and this current distribution of sampling sites might not be representative of the range of demographic and geographic characteristics desired in a national network, nor equitable, optimally actionable, or sustainable. Because 16 percent of the U.S. population resides in unsewered communities, wastewater surveillance in and of itself cannot be fully representative of the population but should be viewed as one key component of a national infectious disease surveillance system.
CDC should take additional steps to bring the benefits of wastewater surveillance to critical areas not addressed by the NWSS. The committee identified three steps that CDC could take to ensure that resources expended on wastewater surveillance systems are not distributed inequitably. First, CDC should create a comprehensive outreach program to provide information to selected public health officials and utility personnel in localities that are not currently using wastewater surveillance about the potential benefits of joining the national system. Second, CDC should reduce financial and staff capacity barriers to joining the system. CDC could reduce barriers by providing continued and expanded funding to state, tribal, local, and terri-
torial health departments and utilities and by creating an easily operable data management and analysis system wherein local wastewater surveillance programs can easily transmit their samples and data for centralized analysis and data visualization (see Chapter 4). Finally, because some areas that are important to understanding national infectious disease transmission will remain outside the wastewater surveillance system even with these resources in place (e.g., in unsewered areas), CDC should assess whether tools can be used to extrapolate data from monitored regions to estimate disease burden in areas without wastewater surveillance. CDC and local health departments should also maintain robust infectious disease surveillance programs using other sources of data on disease trends and provide public education about how to interpret wastewater data alongside other indicators.
As part of a national wastewater surveillance system, strategic incorporation of sentinel sites is recommended as a mechanism for early detection. Sentinel sites should be intentionally selected to monitor for specific emerging pathogens at their points of entry into human communities. Sites that can directly inform community wastewater-based surveillance, especially as related to emerging pathogens, will provide important and distinct benefits in the context of a national surveillance network. Such sentinel sites could include wastewater surveillance at major international airports with a large number of global travelers to detect emerging pathogens and antimicrobial resistance genes. Sentinel monitoring at ports of entry could allow early detection of emerging pathogens entering the country that otherwise may be too dilute to detect at the community scale. Wastewater treatment plants with zoos or major livestock farms that contribute to its sewer system could also serve as valuable sentinel sites to detect the emergence and transmission of zoonotic pathogens. Developing useful sentinel sites will require careful planning and thoughtful experimentation with site selection, program design, and data interpretation based on the pathogen(s) of interest. Sentinel sites are a cornerstone of any public health system, and the NWSS should seek to incorporate these sites in a way that will ensure the surveillance system is nimble and adaptive as needed to address emerging threats.
STRATEGIES FOR ACHIEVING THE VISION
CDC should develop an open and transparent process for prioritizing targets for wastewater surveillance. Selecting future targets for wastewater surveillance is a challenging endeavor that balances potential health benefits against resource investments and the capabilities of existing technology. CDC would benefit from an independent external advisory panel, with representation from industry, academia, and public health, to provide periodic guidance and input to this process and ensure that the latest advancements
in science and technology are considered. The external advisory panel could also provide rapid consultation in future pandemic emergencies. Public input to the process is important because the community should have the opportunity to have concerns heard and considered before a final plan is implemented.
Although the committee judges that the benefits of responsibly managed wastewater surveillance outweigh the associated ethical concerns, CDC should address privacy concerns through clear public communication and by convening an ethics advisory committee. CDC should develop and disseminate additional public communications designed to inform the public about the data generated in wastewater surveillance and how these data are used. In addition, CDC should empanel a standing ethics advisory committee to recommend guidelines about the conditions under which wastewater data may be shared with others and to evaluate future expansions of data collection and data access. It is desirable for academic and industry partners to be able to conduct and contribute analyses of wastewater data, which requires responsible data sharing. The ethics committee, which could be modeled after existing data use committees, should create a formal process for executing data use agreements to help address privacy concerns and alleviate burdens in managing data sharing at a local level. Furthermore, if the prospects for identifying individuals in wastewater data strengthen over time, or if any agency or private-sector organization expresses interest in using wastewater data for purposes other than infectious disease surveillance, this body should re-evaluate the balance of health benefits versus risks associated with data sharing and any proposed expansions in data collection and data linkage. There should be a strong firewall maintained that precludes use of data by law enforcement. In performing its work, the ethics body should consider whether steps are needed to help avoid stigmatization of particular communities or to build further buy-in to wastewater surveillance among members of particular communities.
The effectiveness of the NWSS will depend on predictable and sustained federal investments. The COVID-19 pandemic emergency spurred many researchers and utilities to volunteer their labor and donate resources in support of the effort, but the vision of a sustained national wastewater surveillance system necessitates a shift from volunteerism to a strategic national plan with well-defined roles supported by federal investments. Federal funding is needed to continue to advance sampling and analysis methods and data analysis tools to improve data quality, comparability, and actionability. Predictable funding is also essential to maintain the workforce capacity and institutional knowledge to sustain a well-functioning wastewater surveillance system that is useful to public health agencies and to support an effective system for data management and interpretation for all public health agencies.
Close coordination among public health agencies, analytical laboratories, and wastewater utilities is essential to generate reliable data and support appropriate data interpretation and use. CDC’s Communities of Practice for wastewater utilities, laboratory personnel, and public health practitioners provide valuable support for coordination within each of these fields, and CDC can work with these communities to establish expectations for coordination and collaboration with other agencies. State, tribal, local, and territorial public health agencies should also work to strengthen relationships across these partners—for example, by encouraging biweekly meetings with staff from the public health agency, the analytical laboratory department, and the wastewater utility, as appropriate, in support of data interpretation. CDC, as the nation’s health protection agency, should continue to lead the coordination of the many federal partners in support of this effort.
Because the function of the NWSS depends on the participation of wastewater utilities, CDC and local public health agencies should continue to strengthen relationships with wastewater partners. CDC should continue to work to improve the connections between wastewater utilities and local, state, tribal, territorial, and federal public health agencies, beyond what is currently provided in the Communities of Practice. At a federal level, CDC could set expectations and standards of practice that utilities be engaged as full partners, with compensation for their participation and education and data sharing to ensure that the utilities see the value of their contributions. Local public health agencies should work to build relationships with utilities, who can also provide important expertise essential to developing sound sampling designs and accurate data interpretation.
Looking forward, academia and the broader scientific community are essential to drive innovation in sampling, laboratory analysis, data management and interpretation, and public communication. CDC is commended for launching two initial Centers of Excellence, which will help support targeted research and training. In addition to the Centers of Excellence, CDC should engage the scientific community around specific sampling, analytical, and data management needs through funding mechanisms such as the CDC Broad Agency Announcements. Academic and other research laboratories could provide needed training, and an NWSS workforce needs study would help ensure that a trained workforce can meet current and future needs.