As coronavirus cases and deaths continue to surge in Florida, it’s easy to get lost in the numbers spit out every 24 hours by state government officials.
Coronavirus infections are rising in Florida, and so is the death toll. But understanding the metrics behind these daily reports can be complicated.
The positivity rate, or the percentage of positive tests among the tests processed, has been lifted up by national health experts as a metric key to determining when the spread of the virus is under control. The World Health Organization recommends a state or region maintain a 5 percent positivity rate for at least two weeks before lifting shelter-at-home and social distancing protocols. If an area’s positivity rate is too high, that could mean testing isn’t widespread enough to capture the true spread of the virus.
But doubts over this methodology were raised when dozens of small labs had reported only positive tests and no negatives, inflating their numbers to suggest a 100 percent positivity rate.
Though positivity is helpful for public health experts to track, it’s vital to look at all the data in context, said Dr. Nishant Anand, the chief medical officer at BayCare Health Systems, which operates 15 hospitals around the Tampa Bay area.
Instead of drilling down on specific data coming from a handful of labs, he said the more accurate picture comes from looking across an entire county or the whole state, which offers a much larger data sample.
“You have to take all of these numbers in context together,” Anand said. “I know there’s a lot of focus on the positivity rate, but I view that as one data point.”
1. Positivity isn’t perfect
More than half of all of Florida’s coronavirus tests are processed at just five commercial laboratories: Quest Diagnostics in Tampa, Laboratory Corporation of America based in North Carolina, Bio Reference Laboratories, Inc. based in New Jersey, Genetworx, and Realtox Labs LLC in Maryland.
These commercial facilities are able to process thousands of lab tests a day. Only 15 percent of the remaining 1,100 or so labs reporting to the Florida Department of Health have processed more than 1,000 tests.
Large labs say their numbers are accurate. And because such a big share of the state’s testing comes from just those few facilities, the numbers from smaller labs don’t make a big dent in the end result.
Even when removing all the labs where no negatives were reported, Florida’s percentage of positive tests remains the same - about 12 percent.
“Most of the labs I’ve heard about have been small labs, so the numbers theoretically would be small,” Anand said. “I think looking at the positivity rate across the region is more meaningful.”
Anand used the analogy of students in school. He said he could look at how many children at one school got As, but looking at how many kids in a district got As would widen the data pool and make the sample size much stronger.
Florida’s positivity rate is more than double than the World Health Organization’s 5 percent recommendation. That means there is still disease spread in the community and likely not enough testing, Anand said.
2. Florida puts more emphasis on negative tests
The Florida Department of Health reports the positivity rate in two ways on its daily coronavirus report. One figure comes from the number of people who test positive for the first time “divided by all the people tested that day, excluding people who have previously tested positive.”
That means negative retests are counted while positive retests are not. That shifts more weight onto the negative results, dropping the overall positivity rate. The state also combines both standard coronavirus tests and antigen tests into one catch-all counter. This is troubling because antigen tests, which are used to detect viral proteins and are known for their rapid results, have been found to be inaccurate.
But it’s not possible to know how much the data would change if positive repeat tests were also calculated, experts say. According to the Covid Tracking Project, Florida doesn’t release data related to how many people tested positive for the first time and how many tested positive consecutive times, making it impossible to independently verify.
Anand said like any data point, the positivity rate needs to be looked at in context. He said he likes to consider the actual number of new people tested compared with new positive tests.
“Just like with any fraction, the numbers could be higher or lower depending on what you include in the numerator or denominator,” he said.
3. Data reporting varies between labs
In the state’s daily report, dozens of the same facilities have their testing results spread across multiple line items because of typos, varying names of the lab, or a missing period. The Florida Department of Health said it is working with hospitals and laboratories to standardize the names.
For example, there are five varying monikers for the Orlando VA Healthcare System. It’s listed as “Orlando VAMC,” “Orlando Veteran Affairs Medical Center,” “Orlando VA Medical Center,” and “VAMC Orlando,” in health department reports.
Some facilities enter positive and negative results into the database at the same time, but positive results take priority. In some cases, lab samples are run every hour. The process is semi-automatic, with some manual entry.
Florida Gov. Ron DeSantis said it’s not uncommon for negative results to lag and be reported later than positive tests because the latter is more urgent. In April and May he said some labs unloaded “a huge dump” of negative results after routinely submitting positive tests.
In a July 15 press conference, DeSantis said it’s the law that labs have to report a positive infection for any illness. He said an executive order mandates the labs report negative results as well for tracking purposes.
DeSantis has blamed the reporting issue on the labs repeatedly, saying it’s not the health department’s fault.
“There were a number of labs that were simply doing what the default is,” he said. “I don’t think they were trying to be underhanded, I think that’s sort of what they were doing before this started.”
Positive test results are also reported to each county health department to start contact tracing process, said Lisa Razler, a spokeswoman with BayCare.
4. But even some small labs say they’ve input negative results
Mike Palmer, the CEO of Nona Scientific laboratory in Ocala, wrote in an email to the Tampa Bay Times that all of their data, including negative results, was reported to the Florida Department of Health. However, there were “communication errors.”
Nona Scientific is one of the smaller labs in the state that has reported a 100 percent positivity rate on the daily health department report.
Lori-Ann Martell, the practice administrator for Advance Medical of Naples, also wrote in an email to the Times that they had reported total tests for each day and positive results. Still, on the state report, the lab has a 100 percent positivity rate.
She said it seemed like the error was on the end of the state, but that in the meantime they’ll post their data on their Facebook page for transparency.
“I think everyone is doing their very best in a very busy and stressful time caring for and testing COVID-19 patients,” she said. “Transparency from the testing source is the only way to assure we all understand what is going on in our community/state/country.”
5. So what does it all mean?
Positivity is an important metric, because it shows how common the virus may be in the community and if there’s enough testing to make sure asymptomatic cases are also under control. A high number means testing needs to be expanded.
But it’s not a perfect metric. It only looks at the people who get tested, which includes people who get tested because they think they have symptoms.
Still, health experts rely on it and believe it’s a helpful guidepost for understanding disease in a community - in conjunction with other important data, like looking at new cases, hospitalizations and death.