‘Apples and oranges.’ MS COVID-19 totals are skewed by antibody tests, experts say
Editor’s note: After this article was originally published, the MS State Department of Health started providing a breakdown of positive COVID-19 tests vs. antibody tests. On July 12, less than 4% of 310,897 total tests were antibody tests.
The Mississippi State Health Department is including tests for COVID-19 antibodies in its daily totals on testing and positive cases reported, a practice that overstates the number of tests being conducted and could skew results on infection rates, medical and data experts say.
MSDH communications director Liz Sharlot confirmed Thursday to the Sun Herald that antibody test results have been included in daily testing numbers from the time the antibody tests started being conducted, but she didn’t say when that was.
State Health Officer Thomas Dobbs said 4,055 antibody, or serology, tests are included in the total number of tests. Antibody tests amount to 3.21% of total tests in Mississippi.
Including antibody tests matters because viral and antibody tests show two different things. Viral tests show active infections, while antibody tests indicate past infections.
Including antibody test results artificially inflates the number of tests being conducted and fails to track the active spread of COVID-19, medical and data experts say.
Dobbs doesn’t see a need to track the tests separately.
“It’s such a small percentage of our testing numbers,” he said during Gov. Tate Reeves weekday news briefing Thursday afternoon. “It does indicate infection, it’s just past infection, so it does give us historical perspective about the total number of cases, so there’s value in it.
“We could separate them out. That’s not a big deal. I don’t think it’s an inflation of numbers. It’s just a different mechanism of identifying an infection.”
Viral, antibody tests are ‘apples and oranges’
“You’re putting apples and oranges together and calling them oranges,” Dr. Harry J. Heiman, a clinical associate professor at Georgia State University’s School of Public Health, told the Ledger-Enquirer in Columbus, Ga., a sister McClatchy newspaper to the Sun Herald. “You’re mixing two different tests. . . . All that does is over-inflate the testing number.”
McClatchy was the first to report both tests were being included in a state’s results.
Within hours, the office of Georgia Gov. Brian Kemp asked the Georgia Public Health Department to remove antibody tests from its results.
CNN has since reported that four states have been combining viral and antibody test results, but did not list Mississippi as one of those states. Instead, CNN listed Georgia, Virginia, Texas and Vermont as states where the numbers were being combined.
Mississippi has prided itself on the number of tests done in the state without noting on its website that two different tests are included in its numbers.
Mississippi currently ranks 17th in number of people tested per 100,000, according to state testing data compiled by the COVID mapping project.
The MSDH reported that 125,970 tests had been conducted as of May 20 without differentiating between which tests reflected active COVID-19 infections and which were antibody tests.
MS should separate tests, health data expert says
The state is reporting a total of 12,222 COVID-19 cases and 580 deaths.
T.J. Muehleman, who founded the COVID Mapping Project, said the viral and antibody test numbers need to be separated. He said Georgia is in the process of separating its numbers.
“The reality is that the two tests are testing two different things,” said Muehleman, CEO of the Standard Co, a global health data platform that tracks disease and provides information to organizations in the U.S. and other countries. “They’re two separate types of test and they’re measuring two separate types of things.”
“The reason that we care about the number of tests is because we want to know the number of people who have it now. If we know the number who have it now, we know the people who can potentially transmit it.”
Sharlot said Mississippi is including positive antibody test numbers in its positive case totals.
Dobbs said the positive antibody tests are investigated to determine if the people who tested positive previously had symptoms or were exposed to anyone with COVID-19.
About 80 of the positive antibody tests have been added to overall positive test results, he said.
The problem with that, Muehleman said, is that the epidemiology community is debating the accuracy of antibody tests.
“You’re including potentially wrong data in the pool,” he said, “so that’s another potential issue.”
This story was originally published May 21, 2020 at 2:22 PM.
