Since the coronavirus reached the United States, researchers have struggled to measure how it is spreading.
Some, including a group in Pinellas County, are now looking for an answer in a dark place: the sewer.
Traces of the virus show up in the local wastewater system, said Megan Ross, director of utilities in Pinellas. People shed the coronavirus in their stool, scientists say, which may offer a way to track its prevalence across a large area.
“This is a very new, cutting edge way of looking at viral spread within a community,” Ross said. The county began collecting samples only recently and is trying to find an academic partner to analyze results. “It would be very hard to draw any conclusions at this point,” she said.
The U.S. Centers for Disease Control and Prevention does not know whether the coronavirus spreads among people through feces, though some experts believe the risk is low.
Most sewage ends up in pipes and at treatment plants, where researchers can take samples to look for genetic traces. America’s coronavirus response has been hamstrung by a lack of testing and delays in results. While not everyone can or will get a coronavirus test, scientists say, everyone poops.
“It’s probably a better metric of how many cases we have than the actual testing because if I’m asymptomatic, I’m never going to get tested, I’m never going to become a statistic,” said Timothy LaPara, a professor at the University of Minnesota who studies wastewater microbiology. Even someone without symptoms might shed the virus in their feces.
Research from the Netherlands suggested earlier this year that waste could tip off public health officials to an outbreak, a warning sign before people test positive. Similar studies have started across the world, including in Miami-Dade, building on a surveillance approach that has been used to monitor polio.
In Bozeman, Mont., Blake Wiedenheft, a microbiology and immunology professor at Montana State University, said he took a sample from a wastewater treatment plant and was surprised to find evidence of the coronavirus. His lab has since put out a paper, which is awaiting peer review.
The study, he said, suggests traces show up in sewage after people report experiencing symptoms but before they receive positive results. Health officials have long said testing is a lagging indicator of the disease’s spread because it takes days for patients to notice problems and more time before they get swabbed. Still more days pass before they are officially diagnosed.
Wiedenheft said wastewater tracking is closer to real-time and reveals broadly whether the virus “is trending up or down” in a city, if not necessarily an exact number of cases.
“Within 24 hours you get a result,” he said. The process does not highlight individual infections, and Wiedenheft believes it’s best as a compliment, not a replacement, for regular testing.
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The sewage could further help health researchers track how the virus spreads from place to place, LaPara said. For instance, if it is more present in the wastewater of a tourist town during peak season, that might indicate travel is a contributor to an outbreak.
Pinellas is working with a South Florida-based company called Source Molecular on processing samples, said Bina Nayak, water research project manager for the utilities department. A tool at the wastewater treatment plant pulls samples over the course of a day, she said, and fluid is shipped to the lab.
James Herrin, project manager for Source Molecular, said the samples fill half-liter bottles, which are kept refrigerated or on ice. Lab workers filter the fluid to concentrate it so they can focus just on genetic material of the coronavirus.
Scientists say once the virus is pulled from sewage, the testing process is not much different than what comes after a nasal swab. In the lab in Montana, Wiedenheft said, they can process a sample in about four hours.
Each sample costs Pinellas about $165, Nayak said, and wastewater officials said the money may be reimbursed by the Federal Emergency Management Agency. They are logging results to create an archive for when they find a research partner.
“It’s going to take a lot more work to figure out how to utilize that data on an effective level,” said Ross, the utilities director. “We see ourselves as really an important component in the public health of the community.”
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