Florida cases point to spread
But is the state an “epicenter”? Here’s how to interpret the COVID-19 numbers.
BY IAN HODGSON
Times Staff Writer
As Florida’s coronavirus cases and deaths surged to record levels in July, some national media reports labeled the state an “epicenter” for the disease.
Experts generally shy from using the word epicenter, but is Florida worse off than other states? Are we the outlier?
Delays and varying levels of testing make apples-to-apples comparisons across states and regions challenging.
But looking at the raw number of new cases, the number of new cases per capita and the percentage of people testing positive can provide some context for what’s happening in Florida.
Several data points are stubbornly high, which means Floridians are increasingly at risk of encountering people carrying the virus.
To get a clearer picture, here are some ways experts look at infections, and what the numbers can teach us about the outbreak in Florida.
Cases in Florida are growing fast
The daily number of cases is the data point that makes the most headlines, including when Florida broke a national record with 15,300 reported cases in a single day earlier this month.
It may seem simplistic, but this number is essential for informing policy and public safety decisions, experts say.
“The total amount of cases is important because it speaks to the amount of resources that will be needed to control the epidemic and medical care for the ill,” said Jose Szapocznik, a professor of public health at the University of Miami. However, the new cases reported by the Florida Department of Health can be days or weeks old, and irregular reporting from testing laboratories can lead to dips and bumps in the data. Just such an irregularity may have been behind this month’s record-setting spike.
To help account for these random dips and bumps, experts typically use the average of cases over the past seven days.
“When you smooth over a seven-day period,” said Tom Hladish, an infectious disease researcher at the University of Florida, “you tend to get rid of those weekly artifacts that have nothing to do with disease trans-
mission and everything to do with test processing.”
In Florida, one or two days of newsworthy spikes have given way to daily numbers consistently higher than 10,000 new cases per day. In the past week, 11,000 new cases have been reported each day on average — almost double what the state was seeing at the end of June.
In the past month, Florida has seen nearly 208,000 new infections, or about 10,000 per day on average, more than any other state over the same period.
But the overall state numbers don’t tell the whole story. Instead, we looked at regions that the U.S. Census Bureau calls “core-based statistical areas.” These areas are large enough to average out random noise, but still small enough to give a better idea of where the most concerning hot spots are located.
Looking at the data this way, Florida has three of the 10 fastestgrowing hot spots in the country: Miami, Tampa Bay and Orlando.
The Miami-Fort Lauderdale-West Palm Beach area has seen nearly 76,000 new infections since the beginning of the month, or nearly 4,000 infections per day on average. This is the highest number of any U.S. region.
The Tampa-St Petersburg-Clearwater region is the eighth-highest in the country, with more than 21,000 infections, or nearly 1,200 infections per day, since the beginning of July.
Orlando follows at ninth, with almost 20,000 infections since the beginning of the month.
Florida’s biggest cities have the highest concentration of cases
Just looking at the number of cases can be misleading because places with larger populations will have more cases and 1,000 cases in a large city can look very different from 1,000 cases in a rural town.
Cases per capita is more informative when thinking about your personal risk of infection, said Matthew Hitchings, an infectious disease researcher at the University of Florida. “Higher per-capita infection rate means your risk of having contact with an infectious person is higher.”
Take the examples of Miami and Los Angeles, the two cities with the greatest increase in cases since July 1. Miami has seen 75,000 cases in that time, 25 percent more than the 60,000 in Los Angeles.
However, Los Angeles has nearly double the population of Miami, which means there are more than twice as many new cases per person in Miami than in Los Angeles.
Since July 1, Miami has seen more than one new case for every 100 residents, by far the highest of any high-population area in the country. Among regions with more than 1 million residents, four of the 10 with the highest per-capita infections are in Florida.
Tampa Bay is the seventhhighest of the large regions, with 66 new infections per 10,000 residents.
Experts rely on the number of infections per 10,000 residents when making comparisons across states and countries, said Jeffery Shaman, a professor of epidemiology at Columbia University. However, “those numbers can mean very different things depending on the testing capacity, so it all makes for comparisons across geographies a little challenging.”
To help control for differences in testing rates, experts also look to the percent positive rate.
Even controlling for testing, Florida stands out
Like the number of cases per capita, the percentage of people that test positive for the coronavirus shows how much the virus has infiltrated a population.
“Higher than 10 percent for several days is a dangerous sign,” said Ali Mokdad, a professor of health metric science at the University of Washington, and “you want to see this coming down as you do more tests.”
Testing in Florida has ramped up in the past month, doubling from nearly 30,000 tests per day in mid June to 60,000 in the past week on average. Still, the percentage of tests that returned positive crept up and up, increasing from 10 percent a month ago to nearly 20 percent in the past week.
A percent positive rate of 20 percent means that one infection is discovered for every five tests. Only Arizona has seen a higher percentage in the past month.
However, tracking the percent positive across time or between locations can be misleading. Changes in reporting or testing strategies can affect the results just as much as developments in infections.
“An extreme example would be if a state or county decided to stop testing hospitalized patients and start testing random people on the street,” Hitchings said. “This would drop your percent positive but not in a way that reflects a drop in cases.”
The Florida Department of Health, which releases testing and case data, has come under fire after the South Florida Sun Sentinel reported that the state may be underestimating the percent positive. The Sun Sentinel found that the state may have been double counting negative test results and combining two test types into a single statistic.
Recent reporting has also highlighted misreporting and delays by the testing labs.
Across Florida, the percent positive varies from as high as 30 percent to as low as 10 percent. In both the Miami and Tampa Bay regions, one infection is discovered for about every five tests.
The numbers aren’t perfect, but we should be concerned
Even public health experts like Shaman say it’s frustrating to follow all of these numbers when so much is changing.
“It’s not a random sample of everybody and it’s not ideal from a science perspective,” Shaman said. “But from a public health perspective the primary goal is to use resources as best we can to figure out what’s going on.”
What we do know is that the number of cases in Florida continues to increase and the percentage of people testing positive remains high.
As this trend continues, experts warn that you’re more and more likely to run into someone carrying the coronavirus.
That’s when precautions like social distancing and wearing a mask become even more important, said Hitchings. “The idea of masks is to reduce your probability that, upon meeting an infectious person, you actually get transmission.”
And that’s another thing experts agree on: When the numbers feel overwhelming, the only thing you have in your control is your behavior.
“If we wear our masks, we can open our businesses faster. If we wear our masks, we can delay the onset of the second wave,” said Mokdad. “We do our part to save the economy and save more lives. … I think you get the message.”
Contact Ian Hodgson at email@example.com.