Twice a week at Dallas’ Central Wastewater Treatment Plant in east Oak Cliff, workers use an empty milk jug tied to a string to pull a 250 mililiter sample out of a pool of thick gray water. Two-thirds of Dallas’ waste comes through the plant, so the samples provide a small look at everyone’s, well, poop.
The sample is then sent by FedEx to a lab in Mississippi, where it is tested for levels of COVID-19 on the dime of the U.S. Centers for Disease Control and Prevention.
The CDC has been testing wastewater for the virus since the early days of the pandemic, but Dallas only began participating in the national effort this month. Researchers at the CDC say testing the waste can help provide an early indicator for rising cases and potential new variants, and are trying to expand their monitoring program nationally.
Dr. Amy Kirby, who leads the CDC’s wastewater surveillance program, said data from the water samples allow researchers to monitor not how many people have the virus, but rates of the virus in different communities.
“These data are uniquely powerful because they capture the presence of infections from people with and without symptoms and they’re not affected by access to healthcare or availability of clinical testing,” Kirby said in a recent media briefing. “We’ve already seen examples of cities and counties using their wastewater testing to better understand the trajectory of a surge of infections. Now more communities will have the opportunity to use this tool to help guide their public health decision making.”
Kirby said the CDC expanded its testing program this year to include more 250 more sites — including Dallas.
Phil Huang, the county’s public health director, says it is one more tool the county can use to monitor levels of the virus in the community. It’s not dependent on testing individuals, he said, and is especially effective when at-home tests and asymptomatic cases don’t always show up in official case counts.
“This can be more of an early warning sign if there are increases again,” Huang said. “It’s a way of monitoring things that’s not dependent on tests.”
The CDC posts its data online, but Huang said the small sample size is not yet an accurate picture of how Dallas is doing. He also said it is just one of several factors public health officials will consider when monitoring the ongoing pandemic.
Still, recent numbers of wastewater monitoring nationwide show a slight uptick in wastewater data that could signify an increase in cases in the future. Huang said the county will continue to monitor those numbers along with other metrics.
The fecal testing allows for a community-wide snapshot, Huang said, and can alert public health officials if a new wave or variant of the virus is on the horizon. While people who don’t feel sick may not get tested, and at-home test results aren’t always reported to state officials, the samples tested by the CDC can be a more accurate picture of how the entire county is faring.
“It’s a good sort of systematic way to conduct surveillance on what’s going on,” Huang said.
Yet not everywhere has signed off on the wastewater program. Politico reported this week that many states have either stopped or turned down the CDC’s program, citing cost and privacy concerns from state legislators. In Texas, only sites in Dallas, the Houston area and El Paso are currently sending wastewater samples to the CDC.
Kirby, however, said the expansion of the program will help the CDC’s overall efforts of testing wastewater nationally, and that over half of U.S. states have at least one testing site. She also said this network of fecal testing could be used to track other diseases in the future.
“If you see that a new strain is coming into your community or that the rates and wastewater are starting to go up, you want to take all the same actions — masking, distancing getting vaccinated if you’re not testing if you’re feeling sick,” Kirby said. “But with wastewater, you can start doing those a few days earlier and those extra days really make a difference.”
Charles Scudder, Staff writer. Charlie Scudder is a general assignment reporter and has worked on the features and news desks for seven years. He’s also an adjunct professor at UNT’s Mayborn School of Journalism. Raised in Colleyville, he is a graduate of Southern Methodist University and Indiana University.