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Covid-19 wastewater monitoring is a promising tool, but critical challenges remain

Sewage monitoring stands ready to fill in the gaps and help avoid the threats that an invisible wave of the virus could bring. This monitoring can help identify transmission trends a week or two ahead of clinical testing and gives public health leaders the opportunity to focus on news and resources. It can also be used as a tool to sequence the virus and find new variants earlier.

However, the eagerness to use this tool is stifled by uncertainty about how exactly to do it, along with a lack of resources and support to learn.

Testing wastewater for virus particles can provide early warning signs of increased transmission in a community, even capturing those who have asymptomatic infections or are not tested.

Since the U.S. Centers for Disease Control and Prevention launched the National Wastewater Surveillance System in September 2020, hundreds of sites have come online and still have room to grow. The CDC is funding the program through 2025, and the National Association of County and City Health Officials says interest from its members has grown significantly over the past two years.

But few communities have been able to translate that interest into sustainable practice or concrete action to deal with the pandemic.

Although 38% of local health officials monitored wastewater at some point during the pandemic, only 21% plan to continue to do so after the pandemic has abated, according to a recent report.

Public health officials ranked wastewater monitoring as the least influential factor in pandemic management, and only about half used it in decision-making.

The report presents the results of a survey of more than 200 public health officials across the country, conducted between November and January.

“The thing about wastewater data is that it’s inherently messy,” said Megan Diamond, who leads wastewater work for the Rockefeller Foundation’s Covid-19 Response & Recovery team. The Rockefeller Foundation conducted the survey in conjunction with the Pandemic Prevention Institute and Mathematica.

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An April government watchdog report said wastewater monitoring has “tremendous potential” to be an important public health tool in the US, but noted that some aspects of the science need “further development.”

Wastewater samples can be diluted by rainwater or industrial effluents and contaminated by animal waste, for example.

“As a result, a lot of uncertainty is created, and uncertainty is not the word you want to present to an epidemiologist. It is frightening. It means you have to make a lot of assumptions or research a new science during a pandemic,” Diamond said.

Wastewater monitoring is not a new public health tool, but it was far from mainstream before Covid-19.

According to the survey of public health leaders, public health agencies were most likely to implement wastewater monitoring programs when they had expert support. But about a quarter said there is no clear agency directing this work, and about half said they don’t have the resources or capacity to do it themselves.

“There’s this whole rally around wastewater monitoring, and then the people on the ground, the people actually running the work, say, ‘Yeah, that’s not sustainable for us,'” Diamond said.

The CDC’s introduction of the national sanitation program has helped some, the survey found.

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But it hasn’t come without its own challenges. It took the CDC about a year and a half to figure out how best to standardize the collected data and present it in a national dashboard, a testament to how complicated the data can be.

The agency first unveiled the national dashboard in February, presenting only one data point on the relative change in virus concentration at each site over the past 15 days. Recently the dashboard was updated to include another data point on how the current level of virus detection compares to other points in the pandemic.

However, last month’s Government Accountability Office report found that more work remains to be done.

The agency cited “a lack of national coordination and standardized methodologies” that challenge wider acceptance and hamper efforts to interpret the data and use them to drive public health interventions.

According to the report, it is also unclear how cost-effective wastewater monitoring is. GAO says that wastewater monitoring “can be particularly useful when clinical testing is resource-constrained,” but otherwise raises questions about when it makes sense to use it.

Clinical testing may not be restricted in the US right now, but is underutilized in favor of at-home testing that is unreported or not tested at all.

Current trends in the data are clear: virus levels have been rising at most surveillance sites in the US for weeks. And by the end of last week, more than a third of monitoring sites had detected levels higher than most historical levels, according to CDC data.

Despite the challenges that remain, the benefits of wastewater monitoring shouldn’t be ignored, says Diamond.

“I don’t think we shouldn’t be held back by a lack of consensus on standardizing the data, because that may never happen,” she said.

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