The Centers for Disease Control and Prevention admitted that it is combining viral and antibody tests when reporting its overall testing totals, a decision which scientists say paints an inaccurate picture of the state of the pandemic in America.
The test mix was first reported by NPR’s WRLN station in Miami after a nationwide analysis found major discrepancies between state reports on testing and CDC reports.
“It’s apples to oranges. The two tests measure two different things,” said Mary Jo Trepka, a professor of epidemiology at Florida International University.
“You’ve got to be kidding me,” said Ashish Jha, director of the Harvard Global Health Institute, in a report by The Atlantic. “How could the CDC make that mistake? This is a mess.”
The Atlantic report also found that the CDC is not alone in making the mistake — Pennsylvania, Georgia, Texas, Vermont and other states have also been conflating the results of the two different types of tests. Virginia and Maine only recently stopped.
What exactly is the mistake?
Viral tests — also known as PCR tests due to a process known as polymerase chain reaction — are administered to discover whether someone has an acute, current infection of COVID-19. These tests are what public officials are referencing when confirmed cases are reported.
Antibody, or serology tests, on the other hand, measure whether or not an individual might have come into contact with COVID-19 in the past. They do this by testing an individual’s blood to see if their immune system has developed antibodies in response to the disease.
CDC guidelines note that antibody tests are adequate for research but not for individual use, “i.e., to test people who want to know if they have been previously infected.”
Why does it matter?
By conflating the results of the two tests, the CDC, along with several states, have been making it more difficult to understand the meaning of positive and negative tests.
“The viral testing is to understand how many people are getting infected, while antibody testing is like looking in the rearview mirror. The two tests are totally different signals,” Jha added in The Atlantic report. He added that combining the results makes the date “uninterpretable.”
The conflation also makes it more difficult to judge whether the country or an individual state has improved in their viral testing capacity, since results may be buffeted by the inclusion of antibody tests.
“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,” added Trepka.
It’s important to remember that the test results do not merely amount to a technical error, but have wide-ranging consequences for state and local leaders who make decisions on when to reopen their jurisdictions based on the data.
Since acknowledging the mistake, the CDC is reportedly at work to update its dashboard.
“Now that serology testing is more widely available, CDC is working to differentiate those tests from the viral tests and will report this information, differentiated by test type, publicly on our COVID Data Tracker website in the coming weeks,” CDC spokeswoman Kristen Nordlund told The Hill on Thursday.