How Wastewater Testing Could Help Stop COVID-19 Community Spread

While regularly testing dorm sewage, the University of Arizona detected SARS-CoV-2, the virus that causes COVID-19, in the samples. The university responded with immediate measures to halt a potential outbreak, but the story brought up questions about why urine and stool samples have yet to be added to the COVID-19 testing options.

“This is all actually pretty new,” Aaron Peacock, PhD, director of molecular biology at Microbac Laboratories, Inc, tells Verywell. “It hasn’t really been done on a regular basis...most of these companies that are doing wastewater [testing] are our utility companies, so they’re in cities or counties, or they’re utility districts, and they’re heavily regulated.”

Peacock was not involved in testing the University of Arizona’s dorm sewage, but Microbac Laboratories is currently working with other colleges and universities to test their wastewater for SARS-CoV-2 viral count.

The company is also working with some cities and municipalities that have allotted funding for SARS-CoV-2 testing. Peacock says wastewater testing during a pandemic—and otherwise—can complement other testing methods to give campuses, businesses, and communities a bigger picture of problems ahead. 

Monitoring Community Infection Trends

Testing sewage samples for COVID-19 viral count is different than testing one person at a time. Different models and algorithms could help monitor a general number of active infections in an area, and data could help inform a community about whether infection cases are going up, going down, or remaining the same. 

“If you look at it this way, you’re up in a balloon at 10,000 feet, looking down at the forest, giving you an overall idea of what’s going on in the forest. But when you’re testing individual people, you’re testing individual trees," Peacock says.

Peacock says that SARS-CoV-2 can be shed in a person's feces before they have symptoms.

“It’s kind of a pre-harbinger of what may be coming down the pike for active infections,” he says.

By that logic, the detection of virus particles in wastewater could help communities identify COVID-19 cases sooner, which is what happened at the University of Arizona.

The school’s Water and Energy Sustainable Technology Center tested wastewater from campus residence halls during the first week of in-person classes. They found the presence of SARS-CoV-2 in one dorm. When they tested the students and staff at that location, they identified two individuals who were positive for the virus but did not have symptoms.

As part of the campus's “Test, Trace, Treat” strategy, all students had to have a negative antigen test before they could move into residence halls, according to a statement from the university.

“It’s all about the timing here,” Jagdish Khubchandani, PhD, MPH, MBBS, professor of public health at New Mexico State University, tells Verywell. “I think today, if you test me, hopefully—and most likely—I’m negative. But you leave me alone for three days. In those few days, I may have gone to the local grocery store or met some people and I got infected.”

Catching Cases Before Symptoms

According to research from Johns Hopkins Medicine, when a person is tested in the early days of a COVID-19 infection, the result could produce a false negative.

For the study, which was published in the Annals of Internal Medicine, data from 1,330 samples that underwent reverse-transcriptase polymerase chain reaction (RT-qPCR) testing were reviewed. The researchers calculated daily false-negative rates using the test results and the reported date of infection or the time when symptoms appeared.

By their estimates, individuals who were tested for the virus during the four days after they were infected were 67% more likely to test negative, and therefore receive a false negative. The test proved to be more accurate eight days after infection, but even then, the false positive rate was 20%.

“Even when I get infected,” Khubchandani explains hypothetically, “initially for the first 7 to 10 days—or even two weeks for some people—I have no symptoms, but I still continue to shed the virus.”

The University of Arizona relocated the two students who tested positive for COVID-19 from the residence hall to quarantine. The students will continue classes online until they are able to safely return to dorm life and in-person studies.

If the virus is shed in bodily waste and can potentially be used to detect coronavirus earlier than COVID-19 tests like the nasopharyngeal swab, then why aren’t more schools and communities testing urine and fecal samples?

“Urinalysis would pose additional steps and burden on testing,” Khubchandani says. With testing surges and delays from backlogged labs already an issue, bodily waste testing for individuals would be an additional challenge.

How to Test Wastewater for COVID-19

Peacock explains that Microbac Laboratories obtains a representative sample in one of two ways. The first is what’s called a grab test, where a random sample is collected. The second is a composite test, where an instrument is put in place to collect wastewater every 15 or 20 minutes.

Next, the pH of the sample is adjusted to make the virus particles stick to other particles, which aids in filtering. Then, nucleic acids and potential virus RNA are extracted, and an RT-qPCR test is performed. The test "changes the RNA into the complementary DNA,” Peacock says. “And then that complementary DNA is read by our instrument.” 

The RT-qPCR test is the same analysis that is used for samples collected from nasopharyngeal swabs. However, you need another metric for wastewater testing. Microbac also tests for the pepper mild mottle virus (PMMoV).

“That’s kind of the most abundant human-associated virus in wastewater,” Peacock says. It's also been used to test water quality. “You can use that PMMoV to let you know how much human waste is in the wastewater at any given time,” Peacock says, citing the need to differentiate from human input and industrial input. “And then you can use that to kind of couch your results for your SARS-CoV-2 numbers.”

Testing Beyond Dorms

“Corporations, industries, factories, and work sites can be good places to assess the load of the virus,” Khubchandani says. For example, in the first months of the pandemic, meatpacking plants became COVID-19 outbreak hotspots. Checking for the presence of the virus in a plant’s sewage could help prevent future outbreaks.

Cities might also be able to use the testing to gather data from different subsections of a community. “Wherever you have a lift station (a pumphouse) or an area where the water congregates—[whether] that’s for a neighborhood or for a high school—you can go test that,” Peacock says.

That said, funding and red tape could still be a hindrance. “In a bigger community situation, there’s lots of additional expenditure on enriching the sample to get the right type of viral load. And many cities may not have those types of resources.” Khubchandani says. 

Khubchandani also brings up another important consideration for collecting data. “I think what I have to emphasize is that our biggest challenge with testing sewage water or people is: how do you translate it to public adaption?”

If a community discovers a high COVID-19 burden through sewage testing, then more aggressive social-distancing measures and testing of individuals within that community would have to happen. Khubchandani adds that ultimately, the data is “only useful if there’s a real-time assessment and community action guided by that assessment.”

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