City: Sewage study helps quash outbreak
Researchers with the city, Rice University and Baylor College of Medicine were able to sniff out a potential second outbreak of COVID-19 at a homeless shelter in downtown Houston earlier this year by looking down its drains instead of in people’s noses.
Quashing the resurgence at the Star of Hope Men’s Shelter earlier this year was one of the first successes of an effort to track the novel coronavirus through wastewater, city officials said Thursday. The initiative, one of several occurring around the country, attempts to spot outbreaks by sampling water at city treatment facilities, which could help officials tailor their testing and prevention efforts to specific neighborhoods.
To date, the results from testing wastewater largely have aligned with those from nasal swab testing, said Dr. Loren Hopkins, the city’s chief environmental science officer. That has increased the confidence that the wastewater sampling is accurate. The benefit, she said, is that wastewater tests produce quicker results.
“Ultimately, the goal is to develop an earlywarning system allowing the health department to identify the city’s COVID-19 hot spots sooner and put measures in place to the slow the spread of this virus,” Mayor Sylvester Turner said.
People shed the virus through feces, regardless of whether they experience symptoms. The city was able to detect the virus in the shelter by placing a sampler on
the manhole outside the facility after its initial outbreak of COVID-19, the illness caused by the coronavirus.
The ability to home in on a single building still is limited, Hopkins said. City officials have deployed that strategy for the shelter and the Harris County Jail, and they are trying to acquire more equipment to expand the effort in the fall. The health department plans to begin testing long-term care facilities, for example.
The broader study, which began in May, involves taking samples fromthe city’s 39 wastewater treatment plants. From there, scientists can analyze the data to get weekly snapshots of the viral load in certain areas, Hopkins said.
Those samples are analyzed locally in Rice and Baylor labs, yielding results available the sameweek the samples are taken. That means the data canbe one or two weeks ahead of the results of nasal swab tests on individuals.
Also, the wastewater samples apply to a regional-level population base, so it incorporates people who were asymptomatic or otherwise did not get tested for the virus.
So far, there has been a strong correlation between the viral load in the wastewater and the positivity rates by nasal tests, so the method has not unearthed large swaths of the virus that have gone undetected by tests. Still, that correlation has increased confidence that the wastewater analysis is accurate and can be used as a bellwether for future outbreaks.
From Sept. 7 to Sept. 14, for example, scientists found the virus was increasing in a statistically significant way in the communities served by the Tidwell Timber, Upper Brays and Forest Cove treatment plants, among others, while decreasing in District 23, White Oak and Homestead.
That information, coupled with the local positivity rate and other factors, helped the health department decide where to send strike teams to test people, conduct outreach and provide education about the virus. The city said the waste water study has resulted in more testing at several congregant living centers.
Some of the treatment plants process waste from only a few ZIP codes, giving more localized information. Others, like the 69th Street plant, take in waste from more than a dozen ZIP codes. In those cases, the scientists attribute their findings to the ZIP codes that provide the most waste.
Sampling more manholes and lift stations, where waste is processed before it reaches a treatment plant, would help narrow the scope on certain communities. Hopkins said they are looking to expand that in October.
Similar efforts are underway in California, Arizona and other cities and countries. In some cases, researchers have been able to detect outbreaks in wastewater up to six days before the first confirmed cases were found. The University of Arizona used the method to stifle a dormitory outbreak, according to the Washington Post. Some experts have called for a national effort to track the virus with sewage.
The strategy is not new. Anthony Maresso, a Baylor professor helping lead Houston’s study, said Joseph Melnick, a young researcher at Baylor College of Medicine, started to sample stool in 1962 to look for polio, which ravaged Houston in the 40s and 50s. That work, he said, convinced leaders to administer vaccines earlier, in the summer instead of the fall. It helped end those epidemics and “create the field of environmental virology,” according to Maresso.
“That great legacy continues with this project,” he said.
Lauren Stadler, a Rice engineer who studies wastewater and also is leading the effort, said the breadth of the coronavirus project will help keep the community safer and better prepared.
“Usually when people think of wastewater, the immediate reaction is ‘yuck,’ ” Stadler said. “So, I was thrilled that this project was able to shed light on the incredible value of studying the stuff that goes down the toilet.”