After re-opening started at the end of April, the number of active COVID-19 cases reported by the Tennessee Department of Health bottomed out at 6,749 on May 20th. The increase in cases started ramping up in early June, and increased to 41,715 on August 9th. Since then, active cases have decreased to 37,382 as of August 25th. Note that active cases is the number of people who are confirmed as being currently infected with the virus. New infections are added to this total, and recoveries are removed. Tennessee is one of the few southeastern states that officially track this statistic.
Does that mean the peak for COVID-19 cases in Tennessee is in the past? The answer is maybe. There is some evidence to support this. The first derivative measures the rate of change. If it is positive then cases are increasing. The second derivative indicates whether the change is speeding up or slowing down. Applying these metrics to the weekly average of active cases in Tennessee, the first derivative indicates that active cases started increasing near the end of May, and the second derivative indicates that this increase started accelerating in early June. The point at which a trend speeds up is called an inflection point. From the inflection point, the average weekly number of active cases increased by a factor of five to August 13th. See the graph below.
Using the first and second derivatives, it appears active cases possibly peaked on August 13th. The increase was already decelerating at that point, and the weekly average of the number of active cases has decreased by 1,500 since.
Does this mean the peak is over? Maybe, but there are risks ahead. The biggest one in the near future is the re-opening of schools, colleges, and universities, which has the potential to re-ignite the spread of COVID-19. As Yogi Berra once said, “It ain’t over ’til it’s over.” We should also be careful to not relax our vigilance until active cases are much, much lower. We have a significantly higher number of reported active cases now than in mid-May. Another increase from this higher level would be a much bigger increase in total cases than earlier in the summer.