New Evidence Emerges That CDC Has Been ‘Distorting’ Stats On COVID-19 Testing
The Centers for Disease Control and Prevention — along with several states — is conflating the results of two different coronavirus tests, according to The Atlantic, and in the process making it more difficult, if not impossible, for experts to interpret the data.
As more states look to reopen their economies, the practice is “providing the country with an inaccurate picture of the state of the pandemic.”
The CDC confirmed this week that it is blending viral and antibody test results in reporting positive and negative coronavirus cases. One test diagnoses active infections, while the other detects prior exposure.
Pennsylvania, Texas, Georgia and Vermont also conflate the two test results. Virginia ended the practice last week, and Maine stopped blending the data on Wednesday.
Viral tests “taken by nose swab or saliva sample, look for direct evidence of a coronavirus infection” and “are considered the gold standard for diagnosing someone with COVID-19, the disease caused by the virus.”
A positive result means a patient is actively sick with the virus; a negative means they currently are not infected.
Antibody tests “use blood samples to look for biological signals that a person has been exposed to the virus in the past.”
A positive result from this test means it is likely the patient previously had or was exposed to the virus; a negative result means the individual likely has never been infected with or exposed to the virus at all.
Experts say that blending results from “the two tests makes it much harder to understand the meaning of positive tests, and it clouds important information about the U.S. response to the pandemic.”
Ashish Jha, the K. T. Li Professor of Global Health at Harvard and the director of the Harvard Global Health Institute, expressed shock that the CDC would mix the results: “You’ve got to be kidding me. How could the CDC make that mistake? This is a mess.”
He told The Atlantic: “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 that by reporting the results together, the CDC is making both types “uninterpretable.”
Mixing the results presents several issues for those attempting to interpret the data and advise public health officials and political leaders on how to move forward amid the pandemic.
Reporting both types of tests together creates the illusion that the U.S. is doing more testing than it actually is, potentially leading officials and the public to feel confident in the nation’s ability to detect outbreaks.
The publication reported that “The number of tests conducted nationwide each day has more than doubled in the past month, rising from about 147,000 a month ago to more than 413,000 on Wednesday, according to the COVID Tracking Project at The Atlantic.”
If the apparent expansion in testing is due to more people undergoing antibody tests rather than viral tests — which look for active infections — then the “ability to detect an outbreak is much smaller than it seems.”
Kristen Nordlund, a spokesperson for the CDC, told us that the inclusion of antibody data in Florida is one reason the CDC has reported hundreds of thousands more tests in Florida than the state government has. The agency hopes to separate the viral and antibody test results in the next few weeks, she said in an email.
Also of concern is the potential for distorting the overall infection rate: “Because antibody tests are meant to be used on the general population, not just symptomatic people, they will, in most cases, have a lower percent-positive rate than viral tests,” The Atlantic reported.
Jha said that mixing the results “will drive down your positive rate in a very dramatic way.”
This appears to be playing out, The Atlantic noted: After resuming publishing test data last week, following a hiatus that began on February 29, and changing the method to include data “compiled from a number of sources” rather than only viral tests, the numbers “have also become more favorable."
After reported nationwide tests doubled, "the portion of tests coming back positive has plummeted, from a seven-day average of 10 percent at the month’s start to 6 percent on Wednesday."
The Atlantic reports:
On Monday, a page on the agency’s website reported that 10.2 million viral tests had been conducted nationwide since the pandemic began, with 15 percent of them—or about 1.5 million—coming back positive. But yesterday, after the CDC changed its terms, it said on the same page that 10.8 million tests of any type had been conducted nationwide. Yet its positive rate had dropped by a percent. On the same day it expanded its terms, the CDC added 630,205 new tests, but it added only 52,429 positive results.
“There is no way to ascertain how much of the recent increase in testing is from antibody tests until the most populous states in the country—among them Texas, Georgia, and Pennsylvania—show their residents everything in the data,” The Atlantic concluded.