Wastewater monitoring: how to strengthen and sustain an important public health tool

Wastewater monitoring has gained visibility and credibility as an effective pandemic management tool. Yet despite its promise, its use around the country remains fragmented, and its future unclear, based on the results from a national survey conducted by the Rockefeller Foundation’s Pandemic Prevention Institute and Mathematica.

Today, a year and a half after the Centers for Disease Control and Prevention launched the National Wastewater Surveillance System, the program has supported wastewater monitoring in 560 counties across 44 states plus Washington, D.C. The hundreds of wastewater treatment plants monitored across these counties cover almost 20% of the U.S. population. With expansion to additional sites underway, NWSS provides technical assistance in sample collection and SARS-CoV-2 viral quantification, and access to a data analytics platform.

Critical to expanded implementation of this public health tool is an understanding of how well it works, and what some of the hurdles are to the effective implementation of wastewater monitoring (particularly since an unknown number of state and local health agencies have launched wastewater monitoring outside of NWSS).

The concept behind NWSS seems relatively straightforward: direct federal funding to help states establish wastewater surveillance programs, then use the resulting data to manage and respond to the pandemic. And the theoretical backing for the concept is strong. There has been significant evidence demonstrating the power of wastewater to track changing threat levels and provide an early warning for new threats — such as viral variants — before they become widespread.

In our survey, we set out to ascertain how well current and future needs of health departments align with plans for national wastewater monitoring, and to assess the varying experiences of state and local health departments serving rural and urban communities. We surveyed public health officials across the country, collecting input from 194 local and 12 state agency leaders who, together, represent 101 U.S. counties and one tribal nation across 34 states.

There were some discouraging results: Only 21% of local agencies surveyed said they were likely or extremely likely to conduct wastewater surveillance after the pandemic wanes, compared to 66% of state agencies. And among the local agencies that had not implemented wastewater surveillance, only 7% have what they need to begin doing so.

The good news: We found that both state and local health agencies with wastewater monitoring programs recognize its value for pandemic management. There was large consensus around the unique advantages of this innovative data source: that it doesn’t rely on individual testing, may act as an early warning system, captures asymptomatic infections, and can be used to monitor viral variants.

However, understanding the value of wastewater data did not translate to using it for pandemic management. Officials continue to struggle to interpret wastewater data and synthesize it with other data sources. Instead, they fall back on traditional surveillance metrics that are more familiar — namely, hospitalizations, case counts — despite the gaps and limitations in these data, particularly as at-home testing increases. Another theme that emerged in survey comments from local agency leaders was that they didn’t have access to their own wastewater data (because it was being generated by a third-party lab or retained by the state health department), and so were limited in their capacity to explore it.

The survey also revealed that state and local agencies are not always in step. For example, while most state agencies reported having key supports in place for wastewater monitoring — including funding, buy-in, partnerships, and internal staff capacity — most local agencies lacked these supports. In open-ended comments, several local agencies reported that the state was not communicating with them nor sharing findings from the wastewater data. This is worrisome, given that the premise behind NWSS is that resources provided to state agencies will trickle down to increase the capacity of those at the local level.

Lastly, we found that wastewater programming needs vary between rural and urban communities. Rural agencies can face significant operational challenges compared to their non-rural counterparts. For example, they were less likely to have a relationship with a utility and wastewater testing lab, and they struggled to get timely data from labs.

Yet from an efficiency perspective, rural agencies fared better. In large, urban communities, agencies may need to implement costly upstream sampling to get data on viral burden that are granular enough to inform public health action. But in smaller, rural communities, data generated from sampling at central wastewater treatment plants — which is more cost-effective and sustainable in the long term — may be adequate to inform pandemic management.

Population density also has implications for what features of wastewater monitoring should be optimized (particularly for infectious disease surveillance). Urban centers may need to prioritize developing an early warning system based on wastewater data — for example, by setting up routine sampling and testing at a handful of sentinel warning sites. But for rural communities, early warnings for new threats often come from cities. The first U.S. case of SARS-CoV-2 was detected in Snohomish County — the third-most populous county in Washington — while the first confirmed case of the Omicron variant in the U.S. was identified in San Francisco. As a result, rural communities may be able to prioritize other needs, such as translating wastewater viral concentrations into an estimate of Covid-19 cases in the community.

What can make wastewater surveillance programs more effective?

Based on the experiences of the public health leaders we surveyed, we see two key steps that need to be taken:

First, health agencies generating the wastewater data must know how to use it for pandemic management. Until now, resources have been spent to generate data that at times are not used or usable. Investing in training programs that enable local end-users to access, understand, and interpret their own wastewater data will be critical. Even better would be to equip local public health officials with an analytic tool that integrates their wastewater data with traditional surveillance data, generates a holistic risk score, and alerts officials to when action is needed based on changes in community risk.

Second, funding and other support for wastewater programming should be made available to local agencies. These agencies have been the building blocks and proving ground for wastewater monitoring since the start of the pandemic, yet too often local communities have been left to fend for themselves. Supporting them directly can help ensure that national wastewater surveillance is coordinated and systematized, and yet context-specific and adapted to community needs.

We’re at a pivotal moment, where interest has been piqued in the power of wastewater surveillance, particularly to detect novel pathogens and health threats. How we adapt our national system now to meet the diverse needs of our communities will make or break the future success of this innovative approach to monitor population health.

Aparna Keshaviah is a principal researcher at Mathematica who directs wastewater surveillance, environmental health, and public health research. Megan Diamond is a manager at the Rockefeller Foundation who leads global wastewater surveillance work at the Pandemic Prevention Institute.