One of Patrick Green’s first orders every day is to open a tap and fill a bottle with sludge.
A utility operator in Modesto, a city of nearly a quarter of a million people in California’s San Joaquin Valley, Green’s primary mission is to help keep the city’s sewers afloat and its wastewater treated to an acceptable level of safety. But in recent months, he and his colleagues have added COVID-19 exploration to their job description.
At the treatment plant, where Modesto’s sewer pipes run together, larger objects, including baby wipes that do not need to be rinsed, and car parts, are removed. What is left is fed into a giant vessel, where the solids settle to the bottom. It is from the 3-foot-deep dark sludge that scientists suck samples in their search for SARS-CoV-2, the virus that causes COVID-19.
Across the country, academics, private companies, public health departments and wastewater treatment plant operators have been working on refining a new public health tool, one with applications that can go far beyond COVID. Wastewater monitoring is not a new concept, but the scale and scale of the current pandemic has vaulted the technique over the narrow walls of academic research for wider public use as a crucial tool for tracking COVID-19 increases and variants at the societal level.
Wastewater monitoring is proving to be so useful that many researchers and public health officials say it should become standard practice in the detection of infectious diseases, as is already the case in many other countries. But whether that happens – and which communities will gain access – depends on the nation’s ability to scale up the approach to a great extent and make it viable in communities, rich and poor.
Like many other public health tools, wastewater testing first gained momentum in big cities and university cities with access to research expertise, equipment, and money. The Modesto project provides a glimpse of the challenges and opportunities associated with making this technology available in communities with more limited resources.
“You should inject more resources into places that are underserved, as they have the disproportionate burden of disease,” said Colleen Naughton, an engineering professor at UC Merced who helps set up tests in Merced, Modesto and the surrounding farm towns in the Central Valley. .
William Wong, director of utilities for Modesto, oversees water and wastewater operations. Since early in the pandemic, he has wanted to monitor the city’s wastewater for SARS-CoV-2. It is a natural extension of his work; Safe disposal of excrement is the foundation of public health and modern society. “We have always seen what we do as protecting public health,” Wong said.
For COVID-19 monitoring, wastewater is not subject to the difficult inconsistencies that come with coronavirus testing in humans. Lack of COVID-19 testing has been a persistent problem throughout the pandemic, stemming from supply chain shortages and widespread variation in local government response. Long delays in test results can leave health officials weeks behind in detecting and monitoring infection trends.
Recently, home tests, with results that rarely find their way to public health departments, have spread. And for people living in communities with lower resources, there are incentives not to test at all, said Dr. Julie Vaishampayan, health worker for Stanislaus County, where Modesto is. A positive test can be a big problem for people who cannot take time off work or keep their children out of school.
In contrast, wastewater monitoring is an efficient and relatively low-budget enterprise, less dependent on human intervention. All beavers, as they say, and about 80% of Americans deposit their solids in a sewer system.
Dozens of research projects around the country have shown that the method can be used to accurately track COVID-19 trends over time. And because people throw the virus in their feces before showing symptoms, increases and decreases in infections at the neighborhood and community level can show up in sludge several days before they show up in tests.
Other health problems also leave their mark on feces. Recent research has found that wastewater monitoring is a reliable method of influenza surveillance and common respiratory disease RSV. The Centers for Disease Control and Prevention told KHN that it will soon launch pilot studies to see if wastewater can detect trends in antibiotic-resistant infections, foodborne illnesses and candida aurisa fungal infection.
There are places where wastewater may not be a good way to keep an eye on COVID. It includes communities without sewers; areas with industrial wastewater where treatment techniques can mask the virus; and communities with large fluctuations in population, such as ski towns.
But where they are available, the data has already proven strong. During the winter wave caused by Omicron, California, Colorado, New York and Texas first discovered the variant via wastewater. Central Valley health officials have said wastewater monitoring has assured them that falls in COVID cases are real and not a distorted reflection of falls in reported tests.
In Modesto, wastewater also revealed that the Delta variant remained the dominant strain well into January, weeks after Omicron had taken over elsewhere. That was important, Vaishampayan said, because some of the available treatments that do not work for Omicron are effective against Delta. Her department asked local doctors to continue using the full range of medications, even after other areas had narrowed their treatment arsenal.
Having academic researchers get the program up and running made the effort possible, said Kristynn Sullivan, chief epidemiologist for Merced County, where two test sites are being set up. “We were interested in it theoretically, but certainly would not have had the resources to pursue it,” Sullivan said. “What this allowed us to do is step into something that is groundbreaking, that’s exciting, with fairly limited involvement.”
For the first time in her public health career, Sullivan said, money is not the department’s constraint. What it lacks most are people: In addition to being inadequately staffed after years of budget cuts, it is difficult to recruit workers for the area, Sullivan said, a problem shared by health departments in rural areas around the country.
And the setup took a significant amount of effort, said Naughton, an engineering professor who helped build monitoring programs around the North Central Valley. It involved the coordination of sampling equipment; arranging refrigerators, coolers and ice to preserve the samples; paper jam navigation; coordinating courier; and the complex analyzes required to transform the results of sludge sampling into infection-level infection data.
In a recently released paper, Naughton and colleagues found that urban areas in California are much more likely to have wastewater monitoring than rural areas. Through the monitoring network she’s setting up with colleagues at UC Davis, which includes eight new Central Valley locations, Naughton hopes to help change that. The collaboration is paid for with funds from state and federal grants, CARES Act money and philanthropic donations.
Nearly 700 locations in three-quarters of states now report data to National wastewater monitoring system created by the CDC, including more than 30 California sites. In many states, however, the data are sparse and sporadic. And experts are concerned that the CDC’s dashboard may be misinterpreted because it reflects percentage changes in virus detection with only limited context.
Still, having the national network in the future will be crucial, health officials said, as researchers translate the raw data into useful information and compare trends across regions. But it will require sustained public will and some upgrades to keep it useful, a reality that has prevented them from getting too excited about its prospects.
The CDC program is funded through 2025. The Central Valley initiative has one year of funding, though researchers hope to continue the project through at least 2023.
In Modesto, utilities said they are happy to utilize the feces as long as funding flows. “I love seeing the data used,” said Ben Koehler, water quality control inspector and lead construction operator for the city. “People want to know that their work has a purpose.”