Menu Close

William Wong, director of utilities for Modesto, oversees water and sewage operations. Since early in the pandemic, he’s wanted to monitor the city’s sewage for SARS-CoV-2. It’s a natural extension of his work.

Kaiser Health News reports that across the country, academics, private companies, public health departments, and sewage plant operators have been working to hone a new public health tool, one with uses that could reach well beyond covid.

Wastewater surveillance is not a new concept, but the scale and scope of the current pandemic have vaulted the technique over the narrow walls of academic research to broader public use as a crucial tool for community-level tracking of covid surges and variants.

Sewage surveillance is proving so useful that many researchers and public health officials say it should become standard practice in tracking infectious diseases, as is already the case in many other countries. But whether that happens – and which communities get access – depends on the nation’s ability to vastly scale up the approach and make it viable in communities rich and poor.

Like many other public health tools, wastewater testing initially took off in big cities and university towns with access to research expertise, equipment, and money. The Modesto California project offers a glimpse of the challenges and opportunities involved in making this technology available in communities with more limited resources.

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, said Dr. Julie Vaishampayan, the health officer for Stanislaus County, where Modesto is located. because some of the available treatments that don’t work for omicron are effective against delta. Her department told local doctors to keep using the full range of medicines, even after other areas had narrowed their treatment arsenal.

“You should be injecting more resources in places that are underserved since they have the disproportionate burden of disease,” said Colleen Naughton, an engineering professor at the University of California-Merced who is helping set up testing in Merced, Modesto, and surrounding Central Valley farm towns.

For covid surveillance, wastewater isn’t subject to the tricky inconsistencies that come with testing for the coronavirus in humans. Covid testing shortages have been a persistent problem throughout the pandemic, stemming both from supply-chain shortfalls and wide variation in local governments’ response. Long delays in test results can leave health officials weeks behind in detecting and monitoring infection trends.

More recently, at-home tests, whose results rarely find their way to public health departments, have proliferated. And for people living in lower-resource communities, there are incentives not to test at all, said Dr. Vaishampayan. A positive test can be a huge problem for people who can’t take time off work or keep their kids out of school.

By contrast, sewage surveillance is an effective and relatively low-budget enterprise, less reliant on human whim.

Dozens of research projects around the country have shown that the method can be used to accurately track covid trends over time. Upticks and drop-offs in neighborhood- and community-level infections can appear in sludge several days before they show up in tests.

Recent research has found that wastewater surveillance is a reliable method for monitoring flu and the common respiratory illness RSV. The Centers for Disease Control and Prevention told KHN it will soon launch pilot studies to see whether sewage can reveal trends in antibiotic-resistant infections, foodborne illnesses, and candida auris, a fungal infection.

There are places where sewage may not be a great way to keep tabs on covid. That includes communities without sewers; areas with industrial sewage, where treatment techniques can mask the virus; and communities with huge fluctuations in population, such as ski towns.

But where available, the data has already proven powerful. During the winter surge caused by omicron, California, Colorado, New York, and Texas first detected the variant via sewage. Central Valley health officials have said that sewage monitoring has assured them that declines in covid cases are real, and not a distorted reflection of declines in reported testing.