U.S. airlines are lobbying the government to have TSA do temperature checks in airports. This is a bad idea for several reasons. Not everyone spreading COVID has a fever, not everyone with a fever spreads COVID. The TSA will get both false negatives and positives with poorly maintained equipment. They lack legal authority in the first place.

Airlines say if the government turns someone away for a fever, they’ll refund the customer’s ticket. Making someone with a fever show up at the airport potentially infecting others in order to qualify for a refund seems like a really dumb idea.

Some scientists say smell tests could be a better approach.

“My impression is that anosmia is an earlier symptom of Covid-19 relative to fever, and some infected people can have anosmia and nothing else,” said physician Andrew Badley, who heads a virus lab at the Mayo Clinic. “So it’s potentially a more sensitive screen for asymptomatic patients.”

In a recent study, Badley and colleagues found that Covid-19 patients were 27 times more likely than others to have lost their sense of smell. But they were only 2.6 times more likely to have fever or chills, suggesting that anosmia produces a clearer signal and may therefore be a better Covid-catching net than fever.

Temperature checks were used for SARS, very imperfectly, but SARS didn’t have pre-symptomatic spread. While smell tests won’t catch everyone with COVID-19, “loss of smell is one of the earliest signs of Covid-19 because of how the virus acts.” Unlike with fever most COVID-19 lose sense of smell and most other infections do not cause it.

A Monell analysis of 47 studies finds that nearly 80% of Covid-19 patients have lost their sense of smell as determined by scratch-and sniff tests, Reed said. But only about 50% include that in self-reported symptoms. In other words, people don’t realize they have partly or even completely lost their sense of smell. That may be because they’re suffering other, more serious symptoms and so don’t notice this one, or because smell isn’t something they focus on.

In a recent study of 1,480 patients led by otolaryngologist Carol Yan of UC San Diego Health, someone with anosmia was “more than 10 times more likely to have Covid-19 than other causes of infection,” she said. Nasal inflammation from some 200 cold, flu, and other viruses can cause it, she said, but especially during the summer, when those infections are pretty rare, the chance that anosmia is the result of Covid-19 rises.

Have people sniff “a standard amount of phenyl-ethyl alcohol (which smells like roses) on a swab or stick” and compare to a stick that “could be a blank, to identify people who falsely claim they can smell.”

Like temperature checks, this would require new legal authority. And it would probably require more training for TSA employees than use of a contactless thermometer. It would also be more challenging to administer to young children, who appear to spread the virus much less in any case.