After stepping up the number of coronavirus tests (more than 2,800 so far, with more than 1,100 results still pending), the Florida Department of Health added 112 new cases through Wednesday evening. That is by far the largest single-day jump since Florida first reported infections on March 1st. It also brings the total number of infections in Florida to 328 cases. Part of the spike in new cases could be ascribed to the increased testing taking place, but the numbers are still eye-popping, especially when projecting future infections on an exponential growth curve.

The image at the top of this story shows the growth rate of coronavirus in Florida over the past 18 days. Note the orange trendline extending up and to the right.

Over the next two days, if the current rate of testing remains steady and the infection growth rate continues, Florida could easily surpass 600 cases by the end of the week:

Now let’s take it a step further. Projecting that same exponential growth out another 10 days, through the end of March, we start to see why the situation in our hospitals could quickly get out of hand. More than 15,000 cases could be identified by then:

Yesterday morning, using the same projection method but without the additional day of testing, we projected 10,000 potential cases by the end of the month. But the new cases found on Wednesday bent the curve upward.

For those struggling to understand how we could spend the first two weeks of March with fewer than 100 cases, and end the next two weeks with over 15,000 cases, consider the power of exponential growth, where every infected case infects at least two more people. Then those two new cases infect two more each. The number of cases doubles over a fixed period of time, and before long, we’re talking about a substantial number of people with the virus.

Here’s another way of thinking about the power of exponential growth – The Water Lily Problem:

Imagine a pond where the water lilies double in number every day, and after 30 days, water lilies completely cover the pond.  On what day would the lilies cover just half the pond? 

 

If you answered “Day 15” you’d be wrong, but you wouldn’t be alone. Our mind automatically goes to this answer because we are comfortable with linear thinking.  If the water lilies cover the entire pond in 30 days, then it seems logical that they would cover half the pond in just 15 days. 

 

But of course, if the the lilies double in size every day, then they would only cover half the pond on Day 29. They then double one final time and cover the entire pond on day 30. 

Exponential growth has a way of sneaking up on us because it starts so slow. And that’s exactly what we saw in Florida the first two weeks: slow but steady growth. The cases are not doubling every day, but every few days. Still, that adds up fast.

First a pair of cases, then a few days later, a third case. Then a couple more days, and then, boom! Three more cases, six in total. But the number of cases doubled in less than a week. Still, the numbers were small. Just six! By the next Sunday, it was ten. And by the next Sunday, it had doubled, and doubled, and doubled again, hitting 108 cases by week’s end.

The trend hasn’t slowed this week. We passed the 200 case mark on Tuesday, and we’re on track to surpass 400 cases later today. Exponential growth is happening right in front of us.

Clearly, additional testing is starting to turn up more cases, too, but it’s not yet clear how much of the growth can be attributed to those additional tests versus an actual spike in the infection rate. And of course, the number of new infections could easily outstrip our ability to test that many cases. Either way, the numbers  we are finding right now help illustrate the problem we’re facing.

On the bright side, if we’re following the recommendations of our local, state and national leaders, we’re likely to see the curve start to trend downward at some point, “flattening the curve.” But given the long incubation period of coronavirus – two weeks – we might have to wait until April before we start seeing the fruits of our isolation.

In the meantime, take heart in the fact that health experts are now predicting that there are far more coronavirus cases out there than we know about, which means the vast majority of carriers are asymptomatic.

Coronavirus remains a deadly disease for some, a mild illness for many, and a non-event for others. It’s important to note that we’re not dealing with a zombie apocalypse, but we are trying to reduce the exponential infection rate of a highly contagious virus which, if left unchecked, could easily overwhelm our health care system and endanger those who are most vulnerable to it..