Someone with a lower level of virus might have a lower probability of infecting others, but it doesn’t mean that they can’t. “I don’t think that we have enough data to conclude that people are only infectious when they’ve got really high amounts of virus,” Binnicker says. “I’m pretty comfortable saying that a person is more infectious. “I don’t think that we have enough data to conclude that people are only infectious when they’ve got really high amounts of virus.
That might mean testing a few hundred people multiple times a week with a low-sensitivity test and watching to see if repeated testing could keep the virus from spreading. “It’s always useful to talk about innovative ideas,” he says. “I think the problem was the proposition was put out there without much in the way of supportive data to show that it could work.
It’s also hard to find infectious virus in samples taken around 10 days after symptoms start — and that’s the window of time contact tracing shows that people are most likely to pass the virus to a close contact, Slifka says.
A low-sensitivity test might not flag them, even though they have enough virus that it should. “We’ve all had strep tests where there’s just kind of touches the throat, and we’ve had other nurses who really scrape it — that influences the test,” Binnicker says.
Someone who has lots of virus but doesn’t have symptoms might be less likely to infect another person than someone with lower levels of virus who coughs every so often. “It’s not telling the full story,” says Jen Heemstra, an associate professor of chemistry at Emory University.
Logistical problems aside, Binnicker says he’d like to see more evidence that low-sensitivity tests could actually separate infected people from infectious people and help control the spread of COVID-19.
That way, if he doesn’t get flagged in a test on Monday, he’d be tested again on Wednesday to see if his viral levels rose. “If you can test people frequently enough, and then couple that with a lot of monitoring and data collection, then you can start to really piece together,” Heemstra says. “If you can test people frequently enough …
When Bob gets tested, he has a low level of virus. “He could be on the downward slope, where he’s already cleared it, and would continue to be less likely to transmit,” Slifka says. “Or it could be the opposite, where he has a viral load that’s low and then goes up.
To make the tests likely to flag samples with negligible virus, clinicians could lower the cutoff point for the number of copies they let a sample run through.