Good post. The epidemiological term you are looking for is Inflection Point.
Thank you. I am, in fact, looking for an inflection point. My indication that we have reached one will be that the R squared value starts dropping—meaning that the polynomial function I have been using is no longer adequate to graph the data, and that I need to start deriving an exponential equation to describe the disease course.
I also noticed that I made a mistake in describing the quantitative difference between the polynomial and the exponential equations. I said that they are close within thousands—that should have been thousandths. I was up way too late posting, I should know better!