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Why watch the wastewater? It could be a boon for public health

Two microbiology and health policy experts discuss the potential and pitfalls of a wastewater surveillance system.

Wastewater surveillance, which arose as part of the national response to COVID-19, has proven effective in tracking ongoing outbreaks and the spread of new variants. So much so that experts in academia and government are now posing new questions: Should the system be expanded, and if so, how?

Last year microbial genomics expert Ami S. Bhatt, MD, PhD, and legal and public health ethics expert Michelle Mello, JD, PhD, joined specialists from across the country with expertise in a wide range of disciplines to discuss exactly that. Their mission was to examine the value of wastewater surveillance in tracking, preventing and controlling the spread of infectious diseases -- not just for COVID-19. In January the group, convened by the National Academies of Sciences, Engineering & Medicine, issued a new report, with recommendations for how to move forward and what to keep an eye on.

Bhatt and Mello discussed the potential, and possible pitfalls, of this kind of national monitoring system, and where the research might go from here.

Can you describe the wastewater surveillance system that was built during the pandemic? How did it work?

Bhatt: The current system was put up very quickly in response to COVID-19. Early in the pandemic, wastewater surveillance systems were developed by several municipalities and universities to assess whether detection of SARS-CoV-2 wastewater could help guide public health actions. After preliminary success, the U.S. Centers for Disease Control and Prevention launched the National Wastewater Surveillance System to centralize and coordinate these efforts in September of 2020.

Community-level wastewater surveillance provides aggregate data from homes, businesses and other institutions sharing a common sewer system; its key function is to detect the presence and changing quantities of a pathogen within a larger community. Infected people shed biomarkers of infection into the wastewater system through feces, urine, saliva and other substances. Sampling occurs at treatment plants, and those samples are then sent to labs for analysis. Those data are shared with national, state and local officials to inform public health decisions and interventions.

We now have an interesting opportunity to take this surveillance system that grew beyond its pilot phase in the acute setting, reflect on it thoughtfully, and mold and shape it into something that'll be useful for COVID-19 and other diseases.

Mello: The work now is about making this really amazing, though makeshift, emergency response system into something that's sustainable. To do that, we can increase financial and staffing support as well as educational outreach efforts. It's an opportunity to think about how we can use something good that came out of the pandemic to improve health going forward. 

What can wastewater tell us about disease and public health? 

Bhatt: Wastewater has been used to evaluate infectious disease outbreaks in the past, most notably in the case of poliovirus. Wastewater science has been very informative during the COVID-19 pandemic -- for example, we can tell the degree to which variants are prevalent in certain populations and track the evolution of new variants.

What are some of the ethical and legal challenges of using a national wastewater surveillance system? How would you recommend approaching them?

Mello: The committee identified three big challenges, the first of which is privacy. "Surveillance" is a charged word, especially among communities in our country who don't have a great history with state-sponsored surveillance. It's important to communicate about this system in a way that addresses misconceptions, offers fact-based reassurance about what it does and doesn't do, and involves communities in building systems that can help them.

For instance, when wastewater is analyzed at the community level, it's not currently possible to identify individuals from the human DNA in the water. However, we need to be honest about the fact that identifiability is a moving target, and as scientists get better at putting different data sources together, it becomes increasingly possible to re-identify specific people from genomic information. Communities need to know that there is a process in place to revisit this issue going forward and there are appropriate protections.  

The second challenge is to think about data use, reuse and sharing. The people overseeing the system need to anticipate requests from outsiders (for instance, law enforcement agencies and academic researchers) to use wastewater data. Those requests have to be carefully considered. Sharing data with researchers can accelerate scientific discovery, but use by law enforcement could jeopardize public trust. We recommend walling wastewater data off from law enforcement and convening a committee to assess other requests that includes experts who can evaluate the risk of identifying individuals and stakeholder representatives who can help spot other potential harms to vulnerable groups.

The third challenge is equity. State and local government participation in the system that arose during COVID-19 is voluntary, so not all communities are represented. And, 1 in 6 Americans are not attached to a sewer system in their home, so there's inherent inequity in who is included. We recommend improving representation in the system by increasing participation. To do this, we recommend that the CDC offer further technical and financial assistance to help local health departments bolster their capacity, and we suggest emphasizing educational efforts to help health departments understand the value of wastewater information. We also suggest using statistical techniques to extrapolate information from participating communities to communities that aren't represented in the system.

Bhatt: Providing equitable information for public health decision making doesn't necessarily mean every single person must be measured. For example, the committee discussed the possibility of different types of testing at places like high-volume airports that are seeing a lot of international travelers, or at zoos or livestock farms where infections like new influenza strains may be emerging. Sometimes, this type of representative sampling or targeted sampling can be effective, and the goal is always to find ways to do targeted testing while trying to benefit public health in a larger population.

Photo by Happyphotons

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