If what’s in the sewage is any indication, Stafford County has 10 times as many people walking around with COVID-19 than test results suggest.
Since April, the county has been doing experimental testing at its two wastewater plants to track levels of the virus. It’s a science known as “wastewater epidemiology,” and before anyone pooh-poohs the idea, the technology has been used for decades to detect polio in countries where it hasn’t been eradicated. It’s also used to estimate the prevalence of opioid abuse in American communities, according to the Stat News website.
The Stafford facilities are among more than 100 wastewater treatment plants nationwide—and only four in Virginia—that are participating in a no-cost pilot program to analyze samples for evidence of COVID-19.
“Sewage contains valuable information on human health,” the county posted in a news alert in May, because metabolites—or small molecules—from viruses, bacteria and chemicals are excreted in urine and feces.
With some diseases, evidence of the viruses go down the toilet before people even show symptoms, “meaning sewage can provide an early indicator of disease spread before people start seeking health care,” according to the Stafford news release.
Indicators from last week’s sampling showed some startling results: up to 18 percent of North Stafford’s population—at least in households hooked to county water and sewer—may have the virus, according to Deputy County Administrator Michael Smith.
“This is estimated to be about 17,800 individuals in the North Stafford sewershed that are actively infected and shedding the virus,” Smith wrote to the Board of Supervisors. “That means one out of every five people in Stafford may be infected. I encourage all to remain vigilant and to follow all safety practices.”
Smith noted how the data is analyzed and stressed that things are still in the testing phase. He said the tests look for genome particles which indicate the presence of COVID-19. The concentration of particles is multiplied by the amount of flow for that day, then divided by the number of cells a typical infected person excretes, or sheds, each day to estimate the number of cases in the area served by the facility.
“The number is still in the testing phase,” Smith wrote, “so there is not a lot of confidence in the actual number of cases; however, the presence of the COVID genome and the concentration can be used to determine if the cases in Stafford are increasing.”
When Stafford first tested the wastewaters in April and May, results showed between 3 percent and 6 percent of sewage samples contained the virus. It took samples at its two facilities: Little Falls Run Wastewater Treatment Plant, which serves about 15,000 households in southern Stafford, and Aquia Wastewater Treatment Plant, which serves about 20,000 households in the northern part of the county, said Andrew Spence, Stafford’s communications director.
About 70 percent of Stafford households are on county sewer and water, according to Stafford news release.
Officials didn’t take samples in June and July because of other issues, and when they resumed sampling two weeks ago, the numbers had gone up, Smith said. Those tests showed between 6 percent and 9 percent of samples had the virus.
Then tests from last week showed Little Falls Run’s caseload remained the same, but the rate of cases at the Aquia plant had increased to 18 percent, which resulted in the 17,800-person estimate Smith shared with county officials.
That estimate is 10 times higher than the number of Stafford residents who have tested positive for COVID-19.
Health officials have said for months that the number of people with the highly contagious infection is probably five times higher than the number of positive cases.
Dr. Donald Stern, former acting director of the Rappahannock Area Health District, quoted that number repeatedly during meetings with county officials and virtual town-hall sessions.
Part of the ongoing challenges of COVID-19 is that up to 40 percent of those infected don’t show symptoms—and they’re not likely to be tested, said Allison Balmes–John, spokesperson for the local health district. Still, the number of positive tests in the local health district—which was 4,520 as of the other Wednesday—remains “a good indicator of the overall spread in our community,” she said.
Balmes–John also said the research study Stafford is conducting is interesting, but the local health district isn’t using wastewater data to make decisions.
Jason Towery, director of Stafford Public Works, believes technology like wastewater epidemiology could change all that.
“If coronavirus has taught us anything, it is that you can never have enough tools to fight a public health crisis,” he said in May. “This technology has the potential to assist with heading off and preventing outbreaks of disease.”
The wastewater pilot program is being led by Biobot Analytics of Somerville, Mass. Biobiot works in collaboration with the Massachusetts Institute of Technology and Harvard University, both located in Cambridge, Mass., as well as Brigham and Women’s Hospital in Boston.
Cathy Dyson: 540/374-5425
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