If you watch the news lately (and what else do you have to do?), you probably have heard the next hurdle the country faces is conducting more Covid-19 tests. More testing helps identify people with the virus, including asymptomatic individuals walking around out there who don’t know their contagious. You know, the guy sitting next to you on the bus.
Finding infected people also allows for contact tracing, or finding and testing the people who have been recently in contact with a positive individual.
But how many tests do we need? Some experts say we need a minimum of a 152 tests per 100,000 population per day. In Florida, that is nearly 32,000 tests a day!
Other experts say that the number of positive cases should be at or below 10%. The logic is that if the number of positives are higher 10%, then you are not doing enough testing to capture all the infected people in the community.
Florida residents, up to this point, have done pretty well with social distancing, as the number of new Covid cases have slowly declined, as our tracking models show. But before we really return to normalcy without a vaccine, we need to know who has already had the virus, those who are asymptomatic and those who are still infected.
So let’s first start of how Florida is doing with conducting tests as of today. According to the Covid-19 Tracking Project as of April 24th, Florida has conducted a total of 316,959 new Covid tests.
Florida’s testing got off to a very slow start until March 13th, when 195 tests were made in one day. In total, Florida has a daily average of 5764 tests a day.
This average is a little misleading because it took a few weeks for Florida to get up to speed. So I calculated only the last 23 days, when the state reached its first 10,000 tests in a single day.
Using this time span, the state average 9724 dally tests. This is about the current daily average, but is still significantly below what is needed to meet the minimum levels some that epidemiologists find acceptable: 32,000 daily tests.
But how is the state doing according to the 10% rule? Using this metric, Florida is doing alright. The lastest testing data shows that Florida is right at the 10% level, as shown in the graph below.
The blue line represents the percent of all tests since March 5th. As you can see, the state’s positive rate started out high, then dropped quickly in the first few days. But the testing rate during this point was quite low until March 13th. As the number of new tests ramped up, the percent of positive results skyrocketed to over 20%.
By the end of March, however, the positives began to stabilize as the number of tests also increased as shown by the following graph.
No you are not seeing double! The number of positive tests by the total number of tests is identical to the graph by date. The number of tests increased as time increased.
But the message is the same, positive Covid-19 tests fluctuated as the testing increased and then stabilized around the 10% level. In other words, when increased testing reached a certain level, in this case around 145,000 total tests, the virus’s natural Florida infection level is 10%.
The importance of having a low positive testing rate is in it’s relationship to future deaths. As we all know, no new Covid-19 cases leads to no new deaths. A graphic representation of what happens when the number of positive Covid-19 tests increases is shown below.
Using the Covid-19 Tracking Project testing data, our Cubic Regression Model displays the almost exponential increase in deaths as the number of positive tests multiply. The model predicts that 3.4% of new positive Covid cases will eventually succumb to the virus (US total is 5.7%). That’s three percent too many.
So how is Florida doing when it comes to testing? The national positive test rate is about 20%. So compared as the nation, Florida is doing well in comparison. But it’s not there yet.
If we are going to get back to working, drinking and eating out again we need to significantly increase the number of tests per day. That number is probably closer to at least 20,000 tests a day.
While we are waiting for the vaccine, we need to know who has the virus, who has had it and who has it but has no symptoms. Otherwise, we are fighting this battle blind.