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Vermonters will notice a drop in the state’s test counts for the coronavirus after the Health Department stopped including antibody results.
The state keeps a running count of how many tests it has administeredfor COVID-19, the official name of the disease related to the coronavirus that first started to affect people at the end of 2019.
As of Tuesday, that count exceeded 30,000. An update on the Health Department’s dashboard indicated it would no longer combine result numbers for people trying to determine if they have the disease with those determining if they have antibodies for the disease.
“As of May 16, the total testing numbers decreased by about 1,000 due to a change in reporting data. The ‘total tests’ number no longer includes serology tests (also known as antibody tests) that were being reported by some labs. The ‘total test’ number now only reflects people who were tested for a current COVID-19 infection.”
“Slowly we started seeing serology tests trickle in,” said Veronica Fialkowski, surveillance epidemiologist within the Health Department. Fialkowski is currently serving as the data team lead for epidemiology during the pandemic.
CNN and The Atlantic explored the impact on a national scale, as Georgia, Texas and Virginia did the same with their testing counts. CNN wrote the combination of results might lead to an incorrect depiction of the virus’ spread and can “overstate a state’s ability to test and track active infections.”
Here’s what the decision to remove tests for antibodies from the count means for Vermont.
Why Vermont’s Health Department removed antibody testing from its count
Trying to analyze results from PCR tests, which determine if there are active infections, can be difficult if combined with tests for antibodies.
Fialkowski provided an apples-to-oranges analogy to highlight why they need to be separated: If you’re trying to determine the percent of red apples in a bucket of apples and oranges, you want to only include the apples.
“So that’s what we’re doing now,” Fialkowski said. “Since we’ve removed serology.”
Counting the red apples (positive cases) against all the fruit means you’re incorporating the oranges (antibody tests) into the percentage.
How does removing antibody tests affect Vermont’s count?
Fialkowski broke down how the reduction in test count fit into the larger scope of the coronavirus in Vermont.
“The thousand was about 4% of all tests counted,” Fialkowski said. “And then as we look at the percent positive rate, it really changed it by a fraction of a percentage point. It was very, very low.”
The dashboard won’t show changes for demographics like race, ethnicity, sex and county distribution, which reflect case counts.
“It’s not something that, looking at these numbers now, changes how we would interpret the data,” she said of the decision to separate the test results. “We just knew that moving forward it could.”
Fialkowski chocked this up to an expected increase in testing for antibodies.
Antibody tests more of ‘a coin flip’
You need approval before you get tested for your antibody status.
“And that’s because the clinical use for serology right now is very limited,” said Dr. Clayton Wilburn, a pathologist with the University of Vermont Medical Center. “It really just tells you who’s been infected.”
Patients and providers can discuss testing, he said. If the provider agrees with moving forward, they will make an order for the test and be put in contact with a pathologist.
“If it didn’t meet criteria that we have set up for it, we would not perform the testing,” he said.
There is limited knowledge on how long antibodies last and the ways they can impact transmission to another person, he said. At this point it’s useful to examine spread and impact of the virus, rather than individual patient care decisions.
He said there is a low prevalence for the virus — “about 1 percent of the population in Vermont.” This means even an effective serology test could yield a false positive for antibodies.
“There is a 50% chance, or basically a coin flip, on whether we would believe that result or not,” he said of a positive test.
Understanding of the correlation between antibody tests and immunity status is not completely clear just yet, he said. He cautioned people when making decisions for their own health and others based off the antibody tests.
Contact Maleeha Syed at firstname.lastname@example.org or 802-495-6595. Follow her on Twitter @MaleehaSyed89.
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