After a six-week trial of screening wastewater for the coronavirus, Utah public health officials plan to scale up a program to test sewage flowing into 40 treatment plants serving three-quarters of the state’s population.
The pilot study conducted by Utah’s three major research universities concluded such screening can help in early detection of local outbreaks, monitor overall community infection trends and confirm low infection rates.
Case in point: The study detected a big viral surge in Hyrum’s and Logan’s wastewater the week before Cache Valley’s COVID-19 caseload exploded.
“The initial results show that we can not only detect the virus in sewage but we also can see trends that are broadly consistent with known infection rates in Utah’s communities,” said Erica Gaddis, director of the Utah Division of Water Quality. “We hope that monitoring the sewage can help in prioritizing limited state resources such as mobile testing.”
Such a tool could be of great value because the known COVID-19 infections are believed to be far less than the actual number since up to a quarter of those infected show no symptoms and therefore are unlikely to get tested.
The pilot study launched in April under the direction of Jennifer Weidhaas, a professor of civil and environmental engineering at the University of Utah. Working with colleagues from Brigham Young and Utah State universities and the Utah Department of Health, she collected and tested influent from plants at Logan, Hyrum, Tremonton, Salt Lake City, Snyderville Basin, the Central Valley Water Reclamation Facility, Price, Moab and the Timpanogos Special Service District.
“One thing that has been great," Gaddis said, “is that the three universities were able to work together and standardize their methods.”
While COVID-19 is largely a respiratory disease, infected people shed the virus through urine and feces, which then winds up as influent at treatment plants. The screening method used by the universities looked for the virus’s genetic material, then coupled concentrations with wastewater flow and service area populations.
The screening detected the virus from influent collected at all 10 plants, and in 64% of the 171 samples taken.
In late May, sharp increases of the virus were measured at two Cache County sewage treatment plants about a week before 287 positive tests were reported among workers at JBS Beef Plant in Hyrum. This result indicates the sewage screening can be an effective tool for predicting outbreaks.
The highest viral loads were found in urban areas, while Price and Tremonton barely registered. Tourist communities, such as Park City, showed higher concentrations per capita of virus than other areas of similar density and size.
The water quality division set up an interactive webpage providing graphic representations of the study’s findings relative to each of the 10 plants. Some of the most surprising came from Moab, where two-thirds of the samples carried signs of the coronavirus, even though Grand County had reported very low infection rates during the study window. Those results may reflect the number of visitors who flocked to the southeastern Utah city, which is a gateway to Arches National Park, during part of that study period.
“We saw meaningful declines in Summit County over the course of the study and have seen steady concentrations in Salt Lake County,” Gaddis said. “We have talked to local health departments, and they are supportive of us continuing and expanding the study across the state.”
The state has secured funding to resume the study and will include a total of 40 treatment plants, she said. Thirty plants are large, handling at least 1 million gallons of wastewater a day, while the remaining 10 serve smaller rural communities.