Looking for 'signal of the curve' as COVID hits new Tri-county high

August 24, 2021
Graph showing COVID cases reached a seven day average of 100 for every 100,000 people in Charleston area.
This graph from the MUSC COVID-19 Epidemiology Intelligence Project shows the new record high in the Charleston area.

As the Charleston Tri-county area hits a new COVID high, the leader of the Medical University of South Carolina’s COVID tracking team is looking elsewhere to see what’s likely to happen here.

“It gives us the signal of the curve,” said Michael Sweat, Ph.D., referring to what has happened in other areas that saw an earlier Delta-driven surge and are now seeing conditions ease. The curve is the trajectory of the spread of COVID-19 as case numbers go up and down. 

But right now, the Tri-county area, which includes Berkeley, Charleston and Dorchester counties, isn’t seeing a curve. It’s seeing an arrow going steadily upward. 

In fact, the area just set a new and unwelcome record, with a seven-day average of 100 cases per day for every 100,000 people. Last week at this time, it was 81 cases per day – a record in its own right, smashed in seven days.

But Sweat said this won’t go on forever, basing that on his analysis of previous COVID hotspots. “I think we're going to continue to see increases for a while, but looking at everything that's happened in thousands of counties in other states, there's a clear signal that this is going to decrease. I feel pretty solid on that. But how high it will go here, I don't know.”

Sweat said earlier hotspots got up to between 100 and 200 cases per 100,000 people each day, then began to fall. He predicted cases in the Charleston area may continue to rise through Sept., then plunge in Oct.

It's a mystery why it goes down. I mean, it's probably driven mostly by people getting scared and cutting back, and maybe the virus just burns through the available networks and then kind of runs out of steam.”

But when it’s burning through like it is now, it can reach a lot of people. “It's looking a hell of a lot like people who aren't vaccinated and have not been impacted before are going to get infected at some point. I think the chances are so huge in this wave.”

And unfortunately, some will end up in the hospital. “There's a wealth of people who are unvaccinated,” Sweat said. 

“Some of the people who are unvaccinated have comorbidities and are older. That's leading us to have this closer relationship to cases and hospitalizations. In fact, it's much higher than we saw in the earlier peak. So that’s concerning.”

More than 80% of the hospitalized patients at MUSC Health-Charleston with COVID were unvaccinated when they were admitted, as of Aug. 24.

Sweat is also watching something called the “effective reproduction number” for signs of what the near future may hold. It tracks how many other people an infected person might pass along the virus to, based on calculations including vaccination levels and natural immunity.

“It's one of the better leading indicators, because it starts to tell you when things are slowing down or decreasing,” Sweat said. “In the Charleston area, we haven’t gone below one.” 

That means each infected person is likely to infect more than one other person. “It shows we’re kind of a hotspot right now.”

He encouraged people to do what they can to protect themselves, from getting vaccinated to wearing masks and avoiding crowds, and know that better times lie ahead. “This will go back down. People just need to be reassured and we have to have vigilance to work our way through it."

Get the Latest MUSC News

Get more stories about what's happening at MUSC, delivered straight to your inbox.