DALLAS — With changing public health priorities and a shrinking willingness to take COVID-19 tests at a health care clinic, it could seem as if trying to get an accurate picture of local case counts is a futile exercise.
But public health experts say that collecting case data is critical to understanding community health needs, even if it requires reworking North Texas’ current virus tracking practices.
The missing piece in the COVID data puzzle may lie in Dallas’ poop — and the city need only look a few hours southeast to Houston for the model of how to turn sewage into a viral spread prevention tool.
COVID surveillance needs to focus on systems that don’t require people to report their infections, said University of Texas Southwestern Medical Center professor Dr. Trish Perl. Houston is doing just that with its robust wastewater surveillance system.
“The information that’s coming out now about this surveillance in sewage systems is really very exciting, and it may actually be a novel strategy that we can integrate to not only understand COVID, but potentially to understand other diseases, such as hepatitis A,” Perl said.
Dallas County’s case counts and hospitalizations are climbing as the area navigates yet another COVID-19 wave, this time due to the highly transmissible BA.5 variant. And even those official case numbers, posted to an online dashboard, likely fall short of reality as people increasingly test at home or forgo testing altogether, said Dr. Philip Huang, the county’s top health official.
Federal and local health organizations have adjusted their metrics accordingly. The Centers for Disease Control and Prevention altered their community COVID level indicators to give more weight to hospitalizations and available hospital beds. Likewise, Dallas County looks at a number of statistics beyond just case counts when determining the area’s risk level.
Available hospital beds show how prepared an area is to respond to severe COVID illness, while case data, especially when broken down by neighborhood, could allow departments to preemptively react before a few cases become community-wide outbreaks.
Wastewater might be one of the best — and only — options for getting that data quickly and accurately.
“It’s about prevention,” said Loren Hopkins, Houston Health Department’s Chief Environmental Science Officer. “If we’re already in the hospital and our rates are going up, well, that’s a little bit too late. People didn’t have to get that sick and we could have done something about it.”
Houston’s early wastewater jump
Within a month of the pandemic’s start in the U.S., Hopkins and other Houston scientists began discussing whether sewage could be used to measure the COVID virus alongside standard swab tests.
It’s not the first time researchers have looked to human waste to learn what pathogens are silently lurking. Fecal cell cultures helped track polio in the 1940s, and advanced scientific methods aided in monitoring for hepatitis A and norovirus decades later. Surveilling wastewater seemed like a viable move to scientists across the country as COVID-19 cases rapidly increased.
Partners from the Houston Health Department, nearby Rice University and Baylor College of Medicine jumped into testing whether they could get accurate measures of the COVID virus via fecal matter, and by early July 2020 they felt confident enough in their results to expand the samples across the city.
The team now tests once a week at the city’s nearly 40 wastewater treatment plants, jails, nursing homes and schools, among other locations, and uses the data to target public health interventions to the areas of the city with high viral loads.
In the beginning of the pandemic, the city would send educational resources, masks and pop-up testing sites to at-risk ZIP codes. Once vaccines became available, scientists looked at wastewater data and vaccination uptake rates when deciding where to place vaccine sites.
The data isn’t just for the health department’s internal use, Hopkins said.
“We put it on a dashboard so that the public can make their own decisions,” she said. “It’s like if you have asthma, you might be looking at an air quality alert. For somebody that is nervous or sensitive or in some kind of compromised situation where they want to be careful about COVID, they can look on the dashboard and see what their ZIP code is doing or what their wastewater treatment plant is doing so they can see how much virus is around.”
Wisdom in Dallas’ waste
Nearly two years after Houston started to study its feces, Dallas joined the CDC’s National Wastewater Surveillance System, becoming one of hundreds of participating sites across the country.
The county is pulling two samples twice a week at Dallas’ Central Wastewater Treatment Plant in east Oak Cliff and one sample twice a week at the Dallas Southside Wastewater Treatment Plant near Sand Branch. The number of samples has grown since the testing first started, Huang said.
Still, Dallas’ sample collection pales in comparison to Houston, which pulls more than 100 wastewater samples per week when schools are out of session, and even more during the school year.
The two cities can’t be directly compared, largely because of their wastewater setups. Houston never centralized its wastewater system, meaning that it has far more treatment plants to pull from than areas like Dallas, which has only two.
More testing sites mean more localized results, making it easier for Houston to gather information on specific neighborhoods. If Dallas wants similar data, it will have to test beyond its two current treatment plants.
Perl believes that’s possible.
“If you have one site in Dallas, you could get an overall sense that cases are going up or down,” Perl said. “But you wouldn’t know if your disease is all over Dallas or if it’s just in one particular community in Dallas.”
While it doesn’t have many treatment plants, Dallas does have 15 lift stations across its wastewater system that help move sewage in its journey across the city. Houston pulls from these stations to get hyper-localized data.
Communal gathering and living centers could also be important focus points for North Texas. Testing outside of schools can tip public health officials off to potential outbreaks, better preparing schools to identify and isolate sick children.
Hopkins said that she was initially cautious about testing at schools because she didn’t know if children were using the bathroom there.
“We had to look, though, and in the very first week we got detections,” she said. “We were able to say, ‘You have detections in the school,’ and that was super helpful to the school nurses.”
Huang said Dallas is looking at Houston’s system to see if a similar expansion is feasible. Such systems require employees to take samples, as well as available lab space to do the testing in a prompt manner.
Some other localities are shying away from wastewater testing because of the logistics required to set up such a system. One April study found that, among state and local entities that survey wastewater, only about half used the data when making pandemic management decisions. Agencies also rated wastewater data as the least influential among factors considered in public health responses.
Wastewater is just one of many sources for COVID information. Sequencing COVID samples to learn about new mutations, visits to the hospital from the virus and how many health care workers are available to care for COVID patients are all vital to evaluating how a city is faring.
But scientists remain hopeful that a robust wastewater monitoring system will better arm public health officials in their responses to both COVID-19 and other illnesses moving forward.
Some wastewater researchers in Houston have already shifted their focus from COVID to monkeypox, Hopkins said, and are working to see whether wastewater surveillance could accurately measure the latest virus to vex the U.S. emergency response system.
“The science has been there a really long time,” Hopkins said. “It just took a pandemic to get everybody focusing and working.”
Recommendations for avoiding COVID where risk level is high
• Stay up to date with COVID-19 vaccines, including booster doses.
• Get tested if you notice any COVID-19 symptoms.
• Increase ventilation when indoors by turning on fans or opening windows to increase air circulation.