New COVID tests?

From NewsHub: Coronavirus: New test might detect COVID-19 in just a second, doesn’t involve nose swab.

They get points for a less positive headline than the Reuters original, but

The center said in an initial clinical trial involving hundreds of patients, the new artificial intelligence-based device identified evidence of the virus in the body at a 95 percent success rate.

As far as I can tell, the claim comes entirely from a press release — I haven’t been able to find any more data. What this implies is that Reuters (and NewsHub) don’t have any way to know what “a 95% success rate” actually means.

A COViD test can be wrong in two ways: it can miss actual infections or it can think there’s an infection when there isn’t.  In the New Zealand context, missing only 5% of infections would be doing well.  Thinking 5% of healthy people are infected would make the test useless. We’ve done roughly 500,000 COVID tests so far in New Zealand. If 5% were false positives, that would be 25,000 people incorrectly thought to be cases.

Also, it matters a lot when people are tested, and for what reason. Someone who is currently sick is  more likely to test positive than someone who is  infected but has not developed symptoms.  An initial clinical study will usually involve people whose infection status is known, leaving out  the more important and more difficult cases.

To be fair to the journalists, there’s expert comment in the story that makes some of these points

The amount of virus present in saliva increases as patients get sicker, he said, and a big challenge is to detect in “people who are borderline”.

“It will be a game changer only if we see validation of this technology against the current technology,” he said.

It might also be worth noting that the researcher in  question, Dr Eli Schwarz, has a previous example of overly-optimistic press releases during the pandemic. He is running a trial of the anti-parasite drug ivermectin, describing it as a possible cure.  Unfortunately, the Australian lab experiment that is said to support ivermectin use found that the drug destroyed the virus only at concentrations nearly five orders of magnitude higher than those being used in the trial.