As testing increases, Florida coronavirus cases have jumped — but infection rates have not
Over the past two days, as Florida has continued to relax coronavirus restrictions, the state has reported a worrying surge in COVID-19 cases statewide — with Thursday’s tally of 1,419 new infections representing the largest statewide increase in a single day since the health department began providing daily updates on the novel coronavirus in March.
But the number of new cases is only part of the statewide picture when it comes to determining whether we’re experiencing a second wave of COVID-19 infections. While the overall number of positive cases has spiked in the past two days, the percentage of positive COVID-19 tests — out of all the results reported in a day — has declined over the same time period, as the state provides testing to more people.
“As we test more people and get more results, the positivity rate is going down,” said Alberto Moscoso, communications director for the Florida Department of Health, which produces the daily updates.
The percent of positive COVID-19 test results statewide has fluctuated between 4% and 8% over the past two weeks and was 5.3% on June 3, the health department reported.
Florida reports new COVID-19 cases based on the date when the health department receives test results. But how many results the department receives each day — from state labs and private ones — varies because some labs report within one to two days of processing a test while others can take a week or longer to deliver an answer.
On Thursday, for instance, the department reported receiving 5,247 test results for Miami-Dade — more than three times the number the agency said it received for the county on June 1, which was 1,139 test results.
But while the number of new cases in Miami-Dade on June 1 seemed low at 92, the positive rate was 8.1% — the highest percentage of the two-week period included in the health department’s report.
Two days later, the number of new cases in the county spiked to 280, three times what it had been two days earlier. But the positive rate for Miami-Dade dropped to 5.3%, according to the health department’s report.
More cases is bad, of course. But the percentage of positive cases is another key indicator experts rely on to determine whether the pandemic is worsening.
“We worry, obviously, if there’s more cases,” said Mary Jo Trepka an infectious disease epidemiologist with Florida International University’s Stempel College of Public Health. “But we’re especially worried if the percentage goes up.”
Trepka said fluctuations in reporting test results, and the fact that the health department reports cases based on the date it receives test results as opposed to the date of symptom onset, make it difficult for epidemiologists to measure the effect of policy changes, such as Friday’s Phase 2 reopening of bars and movie theaters outside of South Florida.
“There’s no piece of the data that gives you the whole picture,” she said.
For a more complete though still imperfect assessment of how Florida is doing, Trepka said she recommends looking at a two-week snapshot of positive test rates and the health department’s data on hospital emergency room visits for cough, fever or shortness of breath — symptoms associated with COVID-19.
“If I see that going up,” she said, “it’s very worrisome.”
This story was originally published June 4, 2020 at 6:36 PM.
