A University of South Carolina researcher has developed a mathematical model for the coronavirus that shows the number of cases in the state doubling every 2½ days.

The model predicts the number of cases in the state growing from 1,105 on March 28 to 2,400 on March 31, said its developer, Jim Morris, a research professor and distinguished professor emeritus of biological sciences. Morris is director emeritus of the Belle W. Baruch Institute for Marine and Coastal Sciences.

His model has the number of cases reaching 4,300 by April 2, then more than 16,000 five days later.

The state Department of Health and Environmental Protection said Wednesday that it projects 2,657 cases by April 2 and 8,053 cases by May 2. However, it said that projected data is estimated and may change significantly due to various factors.

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"As the number of cases in the state significantly increases, the method for controlling the disease spread changes from in-depth investigations of every individual case to community strategies,” DHEC physician consultant Dr. Brannon Traxler said in a release.

“Residents should not expect individual notification that they were exposed to a case," he added, "rather everyone should practice social distancing, stay home and stay away from other people if they’re sick, and wash their hands frequently with soap and water.”

The state on Tuesday reported a total 424 cases in 39 counties, including 50 in Greenville County, 19 in Anderson County and nine in Pickens County.

Morris, who does mathematical modeling for natural phenomena like sea-level rise, told The Greenville News that he started developing the model of the trajectory of the number of cases as an academic exercise. But by March 16, he noticed an exponential trend.

“Day by day, I would get another data point and put it on the graph and compare the prediction with the real data,” he said. “And the model was quite accurate. In fact, it was 99% accurate.”

Morris said he assumed that state agencies were doing modeling, too. But as he watched a state coronavirus briefing recently, he said he heard someone say they were just beginning to model the trajectory of the virus.

Alarmed, he sent a letter to Gov. Henry McMaster with his information.

“My model is accurate to date,” he told The News. “And that doubling time has been decreasing."

When he first started out, he said, the number of cases would double in about three days. Then it would double in to 2.7 days, and now it's 2.5 days.

It’s decreasing because as the state does more testing, it’s finding more cases, he said.

“But even if you use a three-day doubling time, it’s frightening where it goes,” he said. “In early April, there will be an explosion of the number of cases.”

From 4,000 it will hit 8,000 in 2.5 days and 16,000 2.5 days after that, he predicted.

Morris said the state needs to prepare by finding alternatives to hospitals, which will “almost certainly” not have enough beds, and by a statewide sequestering in place, with the exception of going to the grocery store and other essential functions.

“The efforts to date to slow the transmission rate are really good. The governor and the mayors have done the right thing,” he said. “But I think people need to stay at home for two weeks. We’ve really got to get a handle on this and do it fast.

"We don’t want to end up being another Italy.”

Initially, Morris said, the impact of such a shutdown would be small because there are many people who are infected but unknown to health officials and even to themselves because they are asymptomatic or have mild symptoms.

But within a couple of weeks, he said, if people follow the rules, the rate of transmission could drop pretty quickly.

“It won’t fall to zero immediately,” he said. “But if we start this now, we can save our hospitals and flatten out that curve that Dr. Anthony Fauci has been talking about.”

Fauci is head of the National Institute of Allergy and Infectious Diseases who recently testified to Congress about the virus and frequently appears in the daily White House briefings.

Morris said that the country should have been testing for months, like South Korea did. There, they performed widespread testing and isolated those who tested positive, resulting in a lower number of cases, he said.

Morris said he didn’t get a response from McMaster and doesn’t know if the governor saw the letter.

The News asked McMaster’s office and the state Department of Health and Environmental Control for comment on the model but hasn’t yet received a response.

Liv Osby is the health writer at The Greenville News. She can be reached at losby@greenvillenews.com, 864-298-4422 or @livgnews.