One way the state monitors community transmission of COVID-19 has not been done in Charleston and some other areas of South Carolina for more than two months.
At least one scientist who tracks COVID-19 locally said they are ‘flying blind” without widespread testing and wastewater surveillance to look for the virus and provide a key indicator of how much is circulating. The Charleston area may actually be in the midst of another surge based on modeling of what data is available, said Dr. Michael Sweat of Medical University of South Carolina. A Clemson University scientist is urging caution as well.
The S.C. Department of Health and Environmental Control said it is working to take over wastewater surveillance testing for the virus from a lab at the University of South Carolina, which has been reporting those results to the National Wastewater Surveillance System at the Centers for Disease Control and Prevention.
“It has been some time, I think, since USC submitted samples to the CDC for reporting out,” Dr. Linda Bell, the state epidemiologist, acknowledged.
A spokesman for USC did not return calls seeking comment.
Wastewater surveillance can pick up trends in virus levels shed in human waste from people who may not have symptoms yet four to six days before it is likely to be picked up by clinical testing, so it can provide an early warning of outbreaks, according to the CDC. It is meant as a complement to other surveillance, but CDC Director Rochelle Walensky praised the testing this year for providing an early signal of outbreaks beginning in the Northeast.
Wastewater treatment plants regularly pull samples for other testing, so it is a matter of taking part of that sample and shipping it off for testing. The labs carefully handle and filter the samples to get something that can be subjected to the same diagnostic testing as patients, said Dr. Delphine Dean, director of the Clemson Research and Education in Disease Diagnosis and Intervention (REDDI) Lab. Bell said it is a recent addition to surveillance but it has value.
“The concept, that wastewater surveillance can be a big benefit to early detection of transmission in a community that does not rely on somebody having to to go a healthcare facility to be tested, it does have really significant attributes in that way,” she said.
According to the CDC’s data, Charleston has not had its wastewater checked for COVID-19 since at least April 7. The same goes for Darlington and Lexington counties, while Richland, Horry, Georgetown and some other areas of the state have not been monitored since around mid-May.
In almost every case, the virus levels were rising when last checked. The only current data is coming from monitoring done at Clemson for Anderson, Greenville, Greenwood and Pickens counties. There, “it is kind of steadily increasing week to week,” Dean said. It is not the explosion of cases seen in some previous surges, with the delta and early omicron variants, but it is rising, she said.
That may also be true for the Charleston area, said Sweat, director of the MUSC COVID-19 Epidemiology Intelligence Project. In its monitoring of Charleston, Berkeley and Dorchester counties, cases per day per 100,000 population increased 10 percent this past week, from 31 to 34, Sweat said.
Recent modeling by Johns Hopkins University and the Institute for Health Metrics and Evaluation suggest that only about 10 percent of actual COVID-19 cases are being picked up by testing due in part to a large amount of home tests. Even using a conservative sixfold multiplier would put the actual cases in the community at 204 per 100,000, or about where cases were during the onslaught of the delta variant last fall, Sweat said.
“We’re in a surge, it’s pretty obvious,” he said. “I think there is a lot of transmission, and it is continuing to go up. Because of vaccination and prior infection, we’re not seeing the same numbers hospitalized and dying” due to better protection against severe disease. That is validated by internal numbers: MUSC closely tracks its own staff who come down with COVID-19 and those numbers are approaching what they were during the delta surge, Sweat said.
Wastewater surveillance would provide a better window into how much virus is actually circulating in the community, he said.
“Having wastewater would be really valuable; there is consensus in the field about that,” Sweat said. When the state stopped widespread testing in favor of home tests, “the value of the case reporting diminished because we were getting vast undercounts. That kind of left us in that flying-blind mode,” he said. Wastewater surveillance for the virus was supposed to help alleviate that, but the area is without it, Sweat said.
“We need it,” he said. “I think it would be valuable to see that.”
It is one reason DHEC is trying to do the testing itself. After meetings over the past week, the DHEC Public Health Laboratory is now working to validate its testing as it prepares to take over the wastewater surveillance, the agency said in a statement to the Post and Courier. That process may continue all summer, DHEC Media Relations Director Ron Aiken said.
But even without it, the state is reporting many other good metrics, such as cases per 100,000 population and hospitalizations, that allow people to know what is happening with COVID-19 in their communities, Bell said.
“We do encourage people to continue to look at the traditional surveillance systems,” Bell said.
U.S. Surgeon General Vivek Murthy, in a White House COVID-19 briefing on June 9, also encouraged people to maintain vigilance. “We are not done with the pandemic,” he said. “The virus is still here.”
Clemson was monitoring virus levels in its wastewater on campus and also closely tracking how many people tested positive on campus so it could validate how valuable the wastewater data was in predicting infections, Dean said.
“It allowed us to build pretty good estimates on how the wastewater relates to total case counts,” she said. Its data allows Dean to estimate that 1-1.5 percent of the population is infected in the areas they monitor. It translates into an elevated level of risk, Dean said.
“That means if you are going to be in an indoor setting with a larger group of people, you’re pretty likely to have someone in there who has COVID, so you should take precautions,” she said.