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Poop tests in sewage might predict coronavirus surge

Scientists across the nation are examining Southern California’s poop — maybe even yours — with the hope of more quickly identifying COVID-19 hotspots and better preparing for future surges. The information could also signal when stay-at-home orders can be safely eased in specific communities.

Untreated sewage has been used for years to track viruses as well as to analyze opioid use by neighborhood. Now the race is on to determine whether it can serve as an early warning system for the new coronavirus, particularly since the small fraction of the population receiving swab tests cannot capture the breadth of asymptomatic infections.

“Testing of every individual is very difficult. But if you have 50,000 people in a community, you may be able to determine the prevalence by testing the wastewater,” said Sunny Jiang, a microbiologist leading a pilot project at UC Irvine to identify COVID-19 in sewage systems.

Two of Southern California’s largest sewage districts — the Los Angeles County Sanitation Districts (serving 5.6 million people) and the Orange County Sanitation District (2.6 million people) — are participating in tests, as are at least three smaller agencies in the region. Those five districts are sending sewage samples to a total of nine different groups of researchers, as close as UC Irvine and USC and as far away as Wayne State University in Detroit and Biobot Analytics in Massachusetts.

It’s suspected that the number of infections far exceeds confirmed COVID-19 cases because many of those with the virus display no signs of infection and haven’t been tested. It’s hoped that the sewage tests can better gauge the magnitude of infection in a given area as well as provide advance notice before swarms of sick people begin showing up at the hospital.

That information, in turn, would provide lead time for quarantine orders, for increasing hospital capacities, and for isolating people who are most vulnerable.

While the number of cases may be leveling off locally and statewide, there is growing talk of another surge in the summer or the fall — at least in part because of social isolation orders being eased.

“Part of the thinking with the testing is that we’d have an early warning before there’s a resurgence,” said Jim Colston, director of water quality at the Irvine Ranch Water District, which is participating in the UC Irvine study.

Past sewage detection

Sewage treatment required by the state eliminates viruses, including COVID-19, according to the California Water Boards. But raw sewage coming into treatment carries evidence of the virus, opening the possibility of testing for it.

So far, studies of whether it’s contagious in raw sewage aren’t definitive but early indications are that it’s “unlikely to present a significant infection risk,” said microbiologist Amy Kirby of the Centers for Disease Control at an April 24 webcast on tracking the disease through sewage.

There are several examples of using sewage as an alert system for viral outbreaks, the best known being Israel’s poliovirus epidemic of 2013.

At the time, the country had been declared polio-free by the World Health Organization. But it’s robust system for testing sewage resulted in an early detection of the poliovirus and “allowed rapid mobilization of a vaccine campaign” before any paralysis occurred in the population, according to a study published in Proceedings of the National Academy of Sciences.

One advantage to sewage testing for COVID-19 is that signs of the virus can show in stool as soon as two days after a person is infected. This is true even though the disease can take up to two weeks for symptoms to manifest in that person, according to David Hirschberg, an infectious disease expert at the University of Washington.

But the effectiveness of the testing for COVID-19 remains uncertain when it comes to providing specific information for health officials and policy makers to act on. Early local results have not provided a clear indication of what more complete testing might show.

The Los Angeles County Sanitation Districts tapped its first samples on April 23 from two of its 11 sewage treatment plants. A study by the agency detected the virus in untreated wastewater going into both plants, according to Mike Hoxsey, manager of the districts’ laboratories.

However, more definitive details remain unclear. Initial results from the University of Arizona found that other compounds in the water interfered with readings, “leading to decreased sensitivity and possibly false negative results” in some samples, Hoxsey said. The district is also sharing samples with five other research groups, including UCI, USC and Wayne State University.

Meanwhile, the South Orange County Wastewaster Authority collected the first round of samples from its three plants on March 29 and sent them to Biobot Analytics, which is working on a sewage testing project with scientists from Harvard and MIT.

“The samples were conclusively negative. But that was a point in time when Orange County’s confirmed cases were only 420,” said agency spokesman Steve Greyshock.

There are now more than 3,000 confirmed cases in the county. The agency, which serves about 500,000 of the county’s 3.2 million residents, has since collected weekly samples to submit to research projects in the future, Greyshock said.

Test problems

Test results may be able to determine which communities have the largest concentration of COVID-19 and show whether those concentrations are increasing or declining. But there are a couple key obstacles to getting precise data about how many people in a particular neighborhood or city are infected at any given point in time.

First, not everybody who’s infected sheds the virus into their stool and University of Arizona’s Charles Gerba said it’s too soon to tell what percentage of people do.

“The data is just coming in and not enough analysis has been done to be able to (estimate) at this time,” said Gerba, who specializes in pathogen detection and is involved with his school’s testing of sewage for the coronavirus.

Secondly, those with COVID-19 can continue to shed evidence of the virus in their stool after the virus has become inactive.

Biobot Analytics is among those who have said early results show that the prevalence of the virus in the population could be 10 times — or more — what current swab testing indicates. But Hirschberg of the University of Washington said Biobot’s preliminary findings are controversial in the science community. Gerba is among the skeptics.

“I have my doubts,” he said. “I think it is an overestimation.”

Source: Orange County Register

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