Late last month, Forsyth County announced that 20% of its COVID-19 tests were coming back positive. It was more than double the rate the state had calculated for the county. The discrepancy wasn't unusual. For several weeks, the county has reported a much higher percent positive rate than the state. That's been confusing to Levi Bennett, a Winston-Salem resident, who asked Carolina Curious for an explanation.
“It's so important to me because people need to know what's actually going on,” he said. “And the disparity, I think, just sows more doubt in a lot of people's minds.”
WFDD's April Laissle spoke with state and local public health officials to uncover the reasons behind the discrepancy.
Why is there such a big difference between the percent positive rates from Forsyth County and the North Carolina Department of Health and Human Services (NCDHHS)?
The county looks at a bigger scope of test results when they calculate that rate. NCDHHS only factors in electronically reported results. They say this is because manually reported results can occur in batches, so it can't be confirmed that positive and negatives occurred on the same day. They estimate that about 20% of all test results are reported manually, and all of those are left out of their calculation. Results from rapid tests are also left out.
Joshua Swift, Forsyth County's public health director, says the county factors in those manually reported results, and those from rapid tests. He says they're able to do this in part because they have an epidemiologist on staff who is able to take a closer look at everything.
“She scrubs the data that we get from the state to make sure that they're all Forsyth County residents, not just people that are tested in Forsyth County,” said Swift. “The state cannot necessarily do that because they're looking out for one hundred counties and not every county has an epidemiologist on staff that can do that.”
How much does this difference really matter?
We know that some agencies use the percent positive rate to help make important decisions.
It's one of the numbers the Winston-Salem/Forsyth County school district monitors, though in a statement they said they don't have a “hard line to serve as a marker of whether to continue” to reopen schools. They also said they could change their minds about that at any time.
Percent positive is also taken into account for the state's county level COVID-19 alert system. The state does not consider the county's calculation when assigning those alert levels. Last month, the state designated Forsyth County orange, in part because it had its rate at 9%; 10% would have landed it in the red tier. At the time, Forsyth's calculation was 20%, more than double what the state had.
Does it seem like officials are worried about this discrepancy?
Forsyth County public health officials have said it's more important to pay attention to the overall trends in the metrics rather than little changes in each individual number. Health Director Joshua Swift says it's pretty clear that viral spread is high in Forsyth County, no matter which calculation you look at. He says the upward trends alone should give citizens enough information to make decisions about safety.
But we also know that changes in individual numbers do matter when it comes to certain guidelines, like the state's county-level alert system. And if the difference is large enough, that could impact decisions citizens make about whether to go to the grocery store rather than have food delivered, for example. So it's important to understand how these rates are calculated, and why they may vary.