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VERIFY: Are increased COVID testing levels driving up the positivity rate?

We know increased testing levels can cause case counts to rise, but in an ideal scenario, what should happen to the positivity rate when testing levels rise?

CHARLOTTE, N.C. — Coronavirus case records continue to fall in the Carolinas as daily case counts accelerate. Both North and South Carolina are also reporting rising positive test rates.

However, we know testing has increased, particularly headed into Thanksgiving, as many sought more peace of mind ahead of holiday gatherings and travel.

Is it possible rising testing levels are driving both of these metrics up?


Is the increase in positive test rate the result of testing levels going up?


We already know it is possible to test more people and find more cases, and that it doesn't always mean the virus is more widespread in the community.

However, the positive test rate (also called the positivity rate) is a metric designed to account for fluctuations in testing levels. The positive test rate is increasing, and health officials have attributed this trend to increased viral spread in the community.


"The percent positivity rate just tells you whether the percentage of the people being tested are positive (for the virus)," said Gibbie Harris, Mecklenburg County's Health Director.

So, a 10% positivity rate means one out of ten people tested for coronavirus has an infection. According to Harris, the higher the rate, the more the virus is believed to be spreading through the community.

Positive test rate could be influenced by changes in testing levels, but, independent of changes in viral spread, it's likely to be in the opposite way that daily case counts are. According to Johns Hopkins University, increasing testing levels should actually cause the positivity rate to go down.

South Carolina's Department of Health and Environmental Control has also noted that high positivity rates, on the other hand, could indicate not enough testing is being done.

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The logic here: As you sample more of the community, you should be finding more healthy people, whose negative tests drag down the positivity rate -- that is if the virus isn't becoming more widespread.

In fact, Harris reports that is exactly what happened for a brief period in Mecklenburg County during the Thanksgiving testing surge.

Credit: WCNC

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"The testing market... got flooded," Harris said, of the days leading up to Thanksgiving. "We saw our percent positivity rate drop because of that."

But that sag was short-lived.

According to Harris, the county is still testing at a high rate, but after the pre-Thanksgiving dip, the positivity rate started trending back up again and is higher than before.

Harris said that indicates that as the county tests more people, a growing percentage of them are positive, which means the viral spread is increasing.

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