Timing of rapid COVID-19 testing seems key to ID those infected

Expert says one rapid test may not be enough with Omicron

WORCESTER, Mass. — Could rapid antigen testing for Covid-19 prolong the pandemic?

The screening tool, used by schools, employers and families to ferret out the infected, should have just the opposite effect. But if used too early in an Omicron infection, rapid tests may not pick up virus in the nasal passages, said Nitika Pai, MD, MPH, PhD, associate professor in the Department of Medicine at McGill University, Montreal, Canada.

“The Rapid Antigen Tests come with this kind of an understanding that you may not be able to pick it up if you’re not really symptomatic,” Pai said.

Covid is most likely not to show symptoms early on. In the case of Omicron, Pai said it appears the variant colonizes the throat first, then the nasal passages.

That’s led some to suggest the Food and Drug Administration recommend throat or saliva swabbing instead of nasal swabbing with the rapid tests -- because there’s always a chance a negative early test with Omicron could turn positive a day or two later.

Pai agrees with the FDA decision, however, not to recommend nasal-swab tests be used for throat-swabbing. There is, for one thing, the potential for injury.

“They can’t be poking these swabs inside if they don’t understand it,” she said. “Yes, saliva will probably give you a better (viral) yield and we can go to a healthcare facility and healthcare professionals can do that for you. That would be much safer.”

But the better way to go, Pai said, especially given the risk of picking up an infection at a healthcare facility these days: if there’s truly a concern for infection repeat the rapid test at 24 and 48 hours -- most especially if symptoms develop.

She suggests employers not rely on single rapid tests to clear workers, if a known exposure has occurred.

“Keep a symptom checker or tracker, ask them to self-report,” Pai said. “The problem is people are not going to report, which we know, and that is the downside of rolling out these (rapid tests). But the thing is right now healthcare systems are super-stretched and we need to focus on those who are really sick.”

Of course, anyone with active Covid-19 -- even if they don’t become sick themselves -- could make somebody else really sick. And with a shortage of rapid tests, repeating may not be an option for some. In that case, if there’s strong suspicion of a serious Covid exposure, Pai said it may be time to get a PCR test.

Unfortunately, for many, that will mean waiting in a long line.