A nationwide analysis of COVID-19 data released this week shows broad discrepancies between what some states are reporting about testing for the novel coronavirus to the public, and what is being reported by the CDC. The analysis lists Florida as “the most extreme case” of testing discrepancies between what the state and the federal government are reporting.
Asked about the discrepancy, the CDC told WLRN that it is lumping together antibody tests along with tests for active COVID-19 infections, in an apparent conflation of its own antibody testing definitions.
“It’s apples to oranges. The two tests measure two different things,” said Mary Jo Trepka, a professor of epidemiology at Florida International University. “It’s more informative to look at the numbers of those two tests separately.”
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Antibodies, or serology, tests are used to measure whether someone might have had contact with COVID-19 in the past. Diagnostic — or PCR — testing measures cases of acute, current infections. The CDC’s guidelines specify that antibody tests are adequate for surveillance and research, but not for individual use.
The antibodies tests are not designed “to test people who want to know if they have been previously infected,” according to the CDC website.
“If they are reporting the numbers of real time PCR tests, plus the number of serology tests together, it’s hard to interpret and hard to know how many people are actually screened for an acute infection,” said Trepka.
The CDC only recently released a dashboard to track COVID-19 cases and testing on a national level. The dashboard makes no mention of antibody tests being included.
Even if traces of COVID-19 are found in an antibody test, those results are not logged by states or by the CDC as “positive” results for an acute infection. Grouping the two together could make it seem that a smaller percentage of people who have received tests are positive with COVID-19, since antibody tests do not measure acute infections at all.
Up until last week, data reported by the CDC explicitly did not include antibody tests, as it explained on its archived website.
But in recent days, that page was changed from tracking "Viral Testing" to simply "Testing." Antibody tests are now included in the data. The percentage of people testing positive for COVID-19 has dropped two percentage points since then.
Up until the release of the CDC dashboard, the COVID Tracking Project, which is run by The Atlantic magazine, was a primary national database for tracking COVID-19 across the nation. The project pulls together data from every corner of the nation into a single clearinghouse, and has been so successful that the White House has cited it in official reports.
When the CDC’s dashboard was released, the COVID Tracking Project, made up of journalists and dozens of volunteers, wrote a white paper analysis, comparing what states were reporting versus what the CDC was reporting.
Several states are listed in the analysis as having “major” discrepancies when it comes to testing data. Those include Florida, California, Texas, Massachusetts, Tennessee, Indiana, Arizona, North Carolina, Colorado and Maryland. For many of these states, the CDC reports far fewer tests than what the state is reporting.
In absolute case numbers, the largest discrepancy came from Florida. But in terms of percentage, Indiana is the biggest deviance, with the CDC reporting 58 percent more tests than the state.
The COVID Tracking Project’s analysis found that, at the time, Florida reported the completion of 691,653 COVID-19 tests. Meanwhile, the federal government listed Florida as having conducted 919,109 tests, for a difference of a 227,456 tests.
That amounted to a 33 percent discrepancy between state and federal sources.
“We thought: Wow, this is actually quite a problem. Because to date, Florida has actually done a pretty good job reporting data about the outbreak, at least from what we could see ,” said Alexis Madrigal, a senior editor at The Atlantic and a manager of the COVID Tracking Project. “Florida is still the only state that provides a line list of every case, which is so far beyond what other states have done.”
If anything, researchers expected the state’s testing numbers to be higher than numbers reported by the federal government, because of delays in reporting data.
In an email, CDC spokesperson Kristen Nordlund said another thing that makes federal numbers higher than state numbers is that the CDC tracks the total amount of tests conducted, rather than the number of people tested, as Florida currently does.
Nordlund added that antibody testing is being tracked by the CDC because “it can tell us who previously had the virus.”
“The data in the COVID tracker on testing is meant to capture all testing that is being done,” she said.
She wrote that the "CDC is working to do an in-depth look at the testing differences with several other states."
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