COVID-19 positivity: How Florida calculates its rate and why that matters

COVID-19 positivity: How Florida calculates its rate and why that matters

ORLANDO, Fla. — Compared to other states, Florida is using a different metric to calculate the rate at which COVID-19 tests come back positive.

That positivity rate can be a major factor in making key decisions with regard to reopening the state, or travel advisories for other states.

In Florida, two positivity rates are reported daily, but officials only use the one that excludes repeat positive tests, which can produce a lower rate.

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Some experts say testing the same people repeatedly can cause statistical problems, whereas testing people only once produces a cleaner data set.

The state calculates positivity rates for new cases only by dividing the number of people whose test results were reported on a given day by the number of people who tested positive for the first time.

That number will always be lower than the daily case positivity, which includes every positive result.

Of the 10 largest health departments in the nation, all of them include every positive and negative test in calculating their positivity rate.

Their rationale for including repeat positive tests is simple: If a person is still testing positive, they’re still capable of spreading the virus. Florida has not followed suit in that regard.

“Sometimes the approach is: I started measuring this way, and I will continue to measure this way for the entire duration of this pandemic, even though we know there were probably better ways to do it,” Orange County Health Officer Dr. Raul Pino said.

Pino warns changing course now would make it difficult to make comparisons with earlier data, although other states have made the change.

However, Epidemiologist Jason Salemi notes, key policy decisions are being made based on the calculation chosen.

“The absolute ‘where are we?’ right now is very different...as we’re making decisions on: When do we maybe consider shutting down schools? When should we consider shutting down a classroom? When should we be concerned?”

Experts say an artificially low rate can make it difficult for tourists to determine if they’ll have to quarantine in their states after visiting Florida.

Other states may require our average positivity rate to be below a certain level. While our data may show that we qualify, theirs won’t.