GREENSBORO — Tests at the city's North Buffalo wastewater treatment plant show a sustained upward trend that residents are shedding — through their stools — particles of the virus that causes COVID-19.
The plant, the only one being tested locally, serves nearly 136,000 people in the north half of Greensboro.
The N.C. Department of Health and Human Services is testing samples from 19 wastewater treatment plants across the state to look for evidence of SARS-CoV-2, the virus that causes the disease. A Charlotte wastewater treatment plant is the only other one in North Carolina showing a "statistically significant increasing trend," according to the state.
People who are infected with COVID-19 shed viral particles in their feces, according to a news release from NCDHHS. Though the particles are no longer infectious in wastewater, they are measurable if enough people are infected.
Phone calls and emails seeking comment from state and local health officials late Thursday afternoon were not returned.
In the news release, state epidemiologist Dr. Zack Moore said: "As the delta variant emerges in North Carolina, it’s more important than ever for us to use all available tools to track the spread of COVID-19 so health officials and members of the public can take action if trends are increasing.
"The recent increases we’ve seen are an important reminder that COVID-19 is still here and still a risk for people who are not fully vaccinated."
Wastewater monitoring detects the virus when it's shed by people who are symptomatic, as well as those who are asymptomatic.
That's important because asymptomatic people are rarely tested. The federal Centers for Disease Control and Prevention estimates that 50% of COVID-19 transmission is caused by people without symptoms.
The North Buffalo plant was among nine testing sites recently added by the state. Testing at a plant in Winston-Salem and 15 others statewide showed a plateau in test results. A facility in Roanoke Rapids showed an increase, but it wasn't sustained.
Since January, NCDHHS has been testing the wastewater samples for SARS-CoV-2 as part of the federal National Wastewater Surveillance System.
The amount of SARS-CoV-2 virus, measured as viral gene copies, can indicate if COVID-19 is increasing or decreasing in a community.
At the North Buffalo site, samples taken June 30 showed less than half a million viral gene copies per person.
In samples taken on July 14, that number had increased to nearly 84 million viral copies per person, according to the state.
Moore said the testing helps track the spread of COVID-19 even as fewer people are getting inoculated.
“This can be an early warning system and allow health officials to take actions to stop the spread if trends are increasing,” Moore said.
According to the CDC, sewage testing has been successfully used as a method for early detection of other diseases, such as polio.
About 40% of the state’s population uses septic systems for wastewater, so even if all wastewater treatment plants statewide were participating, the data would represent six out of 10 people in North Carolina.
If wastewater data shows an unexpected increase in COVID-19 in a community, state health officials will immediately notify the wastewater treatment plant and local health department.
The Winston-Salem Journal contributed to this report.
Contact Kenwyn Caranna at 336-373-7082 and follow @kcaranna on Twitter.