Wastewater testing isn’t just for COVID: Washington expands efforts

It’s not a new practice to use our sewage to search for clues about public health trends. But after almost two years of building up Washington’s growing wastewater surveillance system, state epidemiologists are ready to branch out further.

Epidemiology teams started sampling wastewater in October 2021 — at first at three sites in two counties, with the intention of building an early warning system that could predict COVID-19 surges. Now, the team has expanded to 28 sites in 16 counties, and is talking about beginning to monitor for other viruses, like influenza and RSV.

“Wastewater can be used for a lot of things,” said Breanna McArdle, supervisor for Washington’s wastewater-based epidemiology program. “It’s really exciting when you start digging into it.”

Virologists have spent decades tracking polio in sewage, and some cities, like New Orleans and Houston, have also spent over a year developing wastewater surveillance systems to predict virus waves. Last month, the National Academies of Sciences, Engineering and Medicine also released a report that urged further development and investment in the system.

In King County, the state Department of Health is working with the Brightwater, West Point and South wastewater treatment plants, according to the state’s updated COVID data dashboard, which now includes limited wastewater information. The dashboard shows additional sites in Benton, Chelan, Clark, Franklin, Grant, Jefferson, Okanogan, Pierce, Snohomish, Spokane and Whitman counties.

“Now we’re finding different [coronavirus] strains, but you can measure other pathogens and really look at the health of a system without invading people’s lives,” said David Hirschberg, founder of the Tacoma-based RAIN Incubator laboratory, a biotechnology nonprofit that’s collected sewage samples since 2020. “Once you flush, people are like, ‘I don’t really care about that anymore.’”

The process begins at these wastewater treatment plants, which take sewage from homes and businesses, disinfect it and redistribute it. The King County treatment plants generally send clean water back into Puget Sound (or use it for irrigation) and turn the rest of the organic waste into biosolids, which can be used as fertilizer or soil addition, according to Public Health — Seattle & King County.

For the past two years, state epidemiologists have also been collecting “composite samples” at each treatment plant, or representative samples from the sewage that provide 24-hour snapshots of what’s coming through the wastewater, McArdle said. The samples are shipped to the state’s public health laboratory, where teams extract viral particles, which were transported into wastewater by human feces, she said.

The entire process usually takes about 24 hours. No identifiable personal or medical information is available through the sewage, McArdle said.

About $6.6 million in grants from the Centers for Disease Control and Prevention have supported the state’s wastewater epidemiology program since 2020.

While the state doesn’t solely rely on wastewater data to predict COVID trends, and likely won’t ever, the system recently caught some new observations on virus subvariants.

XBB.1.5, a descendant of the omicron XBB subvariant that caused waves of infection in some parts of Asia last fall, has taken hold in the United States, but Washington hasn’t seen quite the same increase. Last week, however, the state’s molecular epidemiology team noticed a spike in XBB.1.5, state epidemiologist Scott Lindquist said.

“That’s a utility, using very helpful tools we didn’t have before COVID,” he said.

Some local biotechnology researchers, like Hirschberg, have followed similar work for decades. Hirschberg, who has an immunology background, and his team dived into COVID-focused wastewater surveillance during the early months of the pandemic.

RAIN’s efforts lost funding from Pierce County’s health department at the end of 2020, but Hirschberg said last week that his team has continued to collect regular sewage samples since then anyway. He’s in the process of applying for grants to fund sequencing efforts for the data, which would reveal what viral particles — and other organisms — are in the sewage.

“Wastewater can look for so many things — polio, respiratory infections that have an intestinal component,” he said. “COVID is a respiratory disease, but obviously it’s in the digestive tract.”

Hirschberg continued, “We’re learning a lot about COVID, but COVID is really the poster child for a lot of other diseases that are coming our way or are already circulating.”

While state public health teams have been encouraged by the system’s early alerts, McArdle urged the public to interpret data with caution and while taking into account other figures, like statewide hospitalizations.

“It’s only capturing people who are pooping into that system that leads to the wastewater treatment plant,” she said. “People on septic systems are not going to be captured in that residential use [category].”

As a result, trends are specific to each sewershed and don’t reflect the entire state.

In addition, a variety of factors, like how much it rained recently or how many people are served by a sewershed, can also impact wastewater results, McArdle said.

But the wastewater trends are useful as a supplemental tool, something to help fill in the gaps, she said. In November, for example, about 77% of results pointed to an increase in SARS-CoV-2 concentrations in wastewater, meaning community COVID levels were higher.

Statewide hospitalization numbers reflected a similar jump throughout the month, according to the state’s COVID data dashboard. The wastewater tool will be especially helpful to track case trends, now that most Washingtonians use at-home testing, Lindquist added.

“It’s truly early warning,” Hirschberg said of wastewater surveillance’s promise. “By the time people end up in the ER, that’s not early warning. That’s the tip of the iceberg. For everyone that ends up in the ER, there’s a hundred more who are sick or carrying the disease.”

In addition, Lindquist is sure the state no longer needs to count every COVID case in order to know what trends look like.

“I think this, as a tool, as been one of the more accurate in noting the trends,” he said. “And the more representative we become as the more communities do this, the better it is.”

The state’s public health teams are already monitoring wastewater for mpox, too. How long their work continues and how many other viruses they can incorporate depend on funding, McArdle said.

“We need to gain more experience with this for sure,” Lindquist said. “But so far, so good.”