For weeks, we've been hearing all about "flattening the curve."
The idea is if everyone stays home and practices social distancing, the number of COVID-19 cases will increase at a rate that won't overwhelm the health care system.
Governor Gretchen Whitmer's stay at home order has been in place for more than one week, and the number of COVID-19 cases is growing quickly; the state went from two cases on March 10 to 6,500 on March 30. Detroit alone has nearly 2,500 cases as of April 1. Click here to see the latest case count.
It's still too soon to tell if we're flattening the curve.
There will be a lag before we begin to see the effects of social distancing, says David Hutton, an assistant professor of global public health at the University of Michigan.
"It takes about a week for symptoms [of COVID-19] to develop and then another few days for someone to go to a health care provider and get tested, and then a few more for the test results to get back and reported," says Hutton. "Based on what we have seen in China, Italy, and Spain, we see the impact of social distancing in about two weeks in terms of hitting a plateau in new cases."
In order to see if Michigan is flattening the curve, you need to pay attention to the daily number of new cases, not the total number of cases. You have likely heard talk in the news of "exponential growth," which means not just that total cases are going up, but that total cases are growing at an increasing rate.
Or, as University of Michigan Assistant Professor of Health Management and Policy Neil Mehta explains it:
"A nice analogy is how money grows in a fixed interest-earning savings account — that’s exponential growth. Just like the interest rate could be high or low, 'exponential' growth of an infection could still be considered fast or slow growth."
The graph below shows daily new identified cases of COVID-19 in Michigan alongside two exponential growth curves: one that models slower growth, and one that models faster growth. The flatter the actual case increase is, the better.
Check out the graph to see if the state is flattening the curve. It will update as new cases are announced each day.
While this is a helpful reference, there are a lot of factors at play when it comes to measuring the spread of COVID-19, including testing. Michigan has a high number of cases, but is testing at a lower rate compared to other states, so it's difficult to tell how many people actually have COVID-19.
"Michigan, like many other states, can and should do a lot more testing," says Mehta. "As different test kits, including rapid tests, become available, I am optimistic that the state can ramp up testing to an adequate level. However, more testing means more cases detected. And that makes it hard to know if we are flattening the curve.
"I am following trends in COVID-19 deaths and hospitalizations because they are less susceptible to bias from changing testing rates. When we see new daily deaths or hospitalizations start to stabilize and even decrease, that would be a very good indication that we are flattening the curve."
Below is a graph of daily reported number of deaths in Michigan. It will update as new deaths are announced each day.
But just reaching a plateau of new COVID-19 cases or deaths isn't enough to call off social distancing.
"We're going to want to see the cases drop down, not just plateau," says David Hutton. "China waited until there were practically no new cases (about two months). We might not have the patience to wait that long. But, we definitely need the number of new cases to be small enough to be manageable by the public health system.... Today we have thousands of new positive cases and that's too many for our public health system to manage."