Increase in COVID-19 cases in Charlotte due to new antigen test results. Here are details.

A coronavirus data update from state health officials Friday shows an unusually high daily increase of COVID-19 cases in North Carolina due to new antigen tests being included in tallies for the first time.

In Mecklenburg County, state health officials reported a total of 532 new COVID-19 cases, but the vast majority of those positives were from antigen tests. And some are backdated, meaning the 391 new antigen results reported for the county aren’t from a single day. Statewide, officials reported 4,563 antigen positive cases total, going back to late May.

Antigen tests have been used in North Carolina and across the United States for months in the public health response to COVID-19.

In August in Charlotte, the Republican National Convention used a rapid antigen testing system, along with other coronavirus protocols to reduce the risk of spreading the virus among hundreds of attendees. So far, there have been just four known cases linked to the RNC.

But the antigen test results previously were not counted toward cumulative totals in North Carolina.

Without counting the batch of antigen tests added to Mecklenburg’s cumulative case total on Friday, the single-day increase of cases was 141. That’s slightly higher than the 7- and 14-day average of daily new coronavirus cases reported by the state.

Still, local health officials say the spread of COVID-19 in Charlotte and the surrounding area is stable, with the positivity rate at 5.2% as of Sept. 23, the latest data available. The number of people needing hospital-level care for coronavirus complications has been generally falling since late July.

What’s an antigen test?

Just as the N.C. Department of Health and Human Services on Friday updated its COVID-19 online dashboard, Mecklenburg’s health director said the new antigen tests would be considered “probable” positive for the purposes of contact tracing and other public health response.

Unlike the majority of COVID-19 tests administered locally and statewide, antigen tests can deliver rapid results in 15 minutes to determine whether a person has COVID-19, Mecklenburg Public Health Director Gibbie Harris said during a news conference Friday.

Medical experts still view the more widely-used PCR, or molecular polymerase chain reaction, test as a more sensitive and reliable diagnostic tool for COVID-19.

“We continue to expect to treat these (antigen) test results as positive tests,” Harris said. “We continue to contact trace, as well as isolate and quarantine, as if they were a confirmed PCR test.”

People who are presumed positive through antigen testing should then seek confirmation through a PCR test. But that “doesn’t happen very often all,” Harris said.

Each day, Mecklenburg and the state announce the latest case tallies once test results are available. A person who tests positive multiple times is only considered one case and is not counted twice in the totals, according to NCDHHS.

An antigen test “looks for specific proteins on the surface of the virus,” state health officials said in a document explaining the inclusion of the results beginning Friday.

Experts have likened this tool to pregnancy or rapid strep tests, due to their speed and convenience. By contrast, a PCR test— which returns results within 24 to 48 hours in Mecklenburg — “looks for the virus’s genetic material.”

Dr. Katie Passaretti, Atrium Health infectious disease specialist, said the antigen tests are helpful to “weed out” people in groups who might have COVID-19.

“It opens up potential benefits,” Passaretti told the Observer Friday. “People are hoping this can be used so you can feel better about going to concerts, arts events and group gatherings.”

Yet the antigen tests, authorized by the U.S. Food and Drug Administration in May, have a major drawback.

“Positive results from antigen tests are highly accurate, but there is a higher chance of false negatives, so negative results do not rule out infection,” FDA Commissioner Stephen Hahn said at the time.

Antigen tests can offer critical surveillance data, especially as officials quickly monitor how widespread COVID-19 infections may be in a community that’s attempting to resume more activities — like in-person learning for college and K-12 students.

Antigen tests are also used at nursing homes to manage COVID-19 outbreaks, including among both symptomatic and asymptomatic residents, according to August guidance from the Centers for Disease Control and Prevention. They’re best used at the onset of an infection, when a person has higher viral load, the CDC says.

To be effective, antigen testing must be done frequently — as often as every three days to limit the possibility of viral spread, Passaretti said.

“No test is perfect,” she said. “You just have to acknowledge that going in, and knowing the strengths and weaknesses.

To date, antigen positive cases account for about 2% of North Carolina’s nearly 200,000 infections. In Mecklenburg, there’s been 391 such cases — or about 1.4% of the county’s total, state health data shows.

COVID-19 in Charlotte

Mecklenburg’s coronavirus trends continue to signal improvement, with Harris now “cautiously optimistic” the region won’t see a post-Labor Day spike in cases like she previously feared.

“(School) reopenings would not be possible without the hard work and dedication this community continues to show to stay safe,” County Manager Dena Diorio said Friday. “As we continue to reopen, I ask that you continue these efforts and not let your guard down.”

The county’s average positivity rate — which gauges the extent of viral transmission, dropped to 5.2% in the past week — the lowest number since the start of the coronavirus pandemic. And the weekly average number of patients requiring hospital-level care fell to 91, according to county health data.

There have been 28,416 confirmed cases in Mecklenburg as of Friday afternoon, NCDHHS reported. That’s a rate of 260 of cases for every 100,000 residents. About 8 in 10 cases have been released from isolation, county officials said.

The local death toll is 355, with just over half linked to outbreaks at long-term care facilities, such as nursing homes.

This story was originally published September 25, 2020 at 4:56 PM.