RALEIGH, N.C. (WNCN) — How did Durham County shift from the lowest levels of COVID-19 in the community to the highest in just two weeks?

That quick change happened because two numbers got too big.

The latest map from the Centers for Disease Control and Prevention had Durham County shaded orange with high community levels of COVID — the first time in two months that any of the state’s counties was not colored green (with low community levels) or yellow (medium).

“Right now the data is showing us there’s a lot more transmission of COVID 19 and a lot more COVID-19 out there than there was a week or two ago,” said Dr. David Wohl, an infectious disease specialist at the University of North Carolina School of Medicine.

The CDC recommends everyone in orange counties wear masks indoors, regardless of vaccination status, including K-12 schools and other community settings.

Durham County Health Director Rod Jenkins said in a statement the county isn’t recommending a mask mandate, but “we will continue to monitor data, and if we begin to see sustained periods of high case growth, we will work with our city and county leadership to recommend a new mandate if needed.”

There has been a dramatic shift in the colors on the map in just two weeks.

A total of 98 counties were green on the map released May 12, with two — Wake and Hyde — yellow.

By last week, the number of yellow counties grew to 10, including eight in central North Carolina: Alamance, Chatham, Durham, Franklin, Harnett, Lee, Orange and Wake.

And the current map has 15 yellow counties — including four adjacent ones along the Virginia border — along with orange-colored Durham.

But why the change?

It has to do with three rates per capita that work in concert with each other — cases, and two hospital figures — for every 100,000 people that live in that county.

Image: CDC.

The first measuring stick is the number of new cases during the previous week. If it’s below 200, your county has a bit more wiggle room with its two hospital measures — the rate of COVID admissions, and the percent of hospital beds taken by COVID patients.

“If we are seeing official counts of cases going up and being high, it’s even an underestimate of the true burden,” Wohl said, pointing to the abundance of at-home tests that seldom factor into those official totals.

But if that case rate is 200 or higher, it’s impossible for your county to be green. In that case, you’re yellow if you admitted fewer than 10 COVID patients into hospitals and have COVID patients in fewer than 10 percent of hospital beds.

That’s what happened to Durham County, where the case rate for every 100,000 people was 217 and it admitted 10.3 COVID patients per capita into hospitals.

“Hospitalization is really key, because you don’t fudge that,” Wohl said.

So why has Wake County been stuck in the yellow zone?

Its case rate is well above that magic number of 200 — most recently, the county had nearly 330 cases for every 100,000 residents — but its hospital measures have been low enough to keep it out of the orange zone.

The CDC says Wake County had just 6.6 hospital admissions per capita over the past week and only 4.2 percent of its hospital beds were occupied by COVID patients.