'This is a mess': CDC, 4 states combine viral and antibody results, skewing COVID-19 data

The CDC is combining viral and antibody COVID-19 test results, potentially overstating the nation's ability to test people for the illness, The Atlantic reports.

The agency confirmed to The Atlantic May 20 that it is mixing results. States have based reopening guidelines on the CDC data.

Pennsylvania, Texas, Georgia and Vermont were also compiling data the same way. Virginia and Maine recently separated its data; Vermont authorities claimed they weren't aware they were mixing data. On May 19, Texas Gov. Greg Abbott denied that the state was blending results, but the Dallas Observer reported it is still doing so.

The practice means it is difficult to know how much the country's ability to test for current COVID-19 cases has improved. A positive viral test confirms an active COVID-19 case, while antibody tests use blood samples to look for biological traces of past exposure or infection. 

"How could the CDC make that mistake?" Ashish Jha, MD, professor of global health at Cambridge, Mass.-based Harvard University and director of the Harvard Global Health Institute, told The Atlantic. "This is a mess."

By combining the two kinds of results, the CDC made both "uninterpretable," Dr. Jha said. If part of the nation's gain in testing has come from antibody test expansion instead of viral tests, its ability to detect an outbreak would be worse than it seems. 

"If you put the two tests together, you fool yourself into thinking you've done more testing than you have," said Elizabeth Cohen, CNN's senior medical reporter. 

The inclusion of antibody data is one reason the CDC has reported hundreds of thousands more tests in Florida than the state government, agency spokesperson Kristen Nordlund told The Atlantic. The CDC hopes to separate the viral and antibody test results in the next few weeks, Ms. Nordlund said.

The CDC stopped publishing complete daily test results Feb. 29. When it resumed publishing last week, a website page said only viral tests were included. On May 20, that language changed, removing all reference to disaggregating the two tests.

More articles on public health:
Global COVID-19 stats: US makes up 31% of all cases
7 states with fastest, slowest spread of COVID-19
South at risk of 2nd COVID-19 wave; virus doesn't spread easily on surfaces — 7 updates

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