Could a Covid-19 odor test help bring the coronavirus under control?

In a perfect world, the entrance to every office, restaurant and school would offer a coronavirus test – one with absolute accuracy, and able to instantly determine who was virus-free and safe to admit and who, positively infected, should be refused.

This reality does not exist. But as many countries struggle to regain some semblance of normal life amid the uncontrolled spread of the virus, some scientists believe that a rapid test made of little more than a stinky strip of paper could at least bring us closer.

The test does not look for the virus itself, nor does it diagnose the disease. Rather, he is looking for one of the hallmarks of Covid-19: loss of smell. Since last spring, many researchers have come to recognize the symptom, also known as anosmia, as one of the best indicators of an ongoing coronavirus infection, able to identify even people who don’t. would not feel sick otherwise.

An odor test cannot report people who contract the coronavirus and never develop symptoms at all. But in a study that has yet to be published in a scientific journal, a mathematical model has shown that sniff-based tests, if given widely enough and frequently, could detect enough cases to dramatically reduce transmission. .

Smell tests could work as a point of entry screen on college campuses or in offices, perhaps in combination with a rapid viral test

Daniel Larremore, a public health researcher at the University of Colorado, Boulder, and lead author of the study, stressed that his team’s work was still purely academic. Although some scent tests are already in use in clinical and research settings, the products tend to be expensive and time consuming to use and are not widely available. And in the context of the pandemic, there is no real data yet to support the effectiveness of scent tests as frequent screening for coronavirus. Given the many testing issues that have hampered pandemic efforts so far, some experts doubt that scent tests can be distributed widely enough or cheat-resistant enough to reduce the spread of infection.

“I have been intimately involved in the fight to have loss of smell recognized as a symptom of Covid from the start,” said Dr Claire Hopkins, ear, nose and throat surgeon at Guy’s Hospitals and St Thomas in UK and recent commentary author on the subject in The Lancet. “But I just don’t see any value as a drug test.”

A reliable odor test offers many potential benefits. It could catch many more cases than fever checks, which have largely failed as a Covid-19 screening tool. Studies have shown that about 50 to 90% of people who test positive for the coronavirus experience some degree of measurable odor loss, a result of the virus wreaking havoc when it invades cells in the airways.

“It’s really like the virus is in your nose right now,” said Danielle Reed, associate director of the Monell Chemical Senses Center in Philadelphia. “This complements a lot of the information you get from other tests.” Last month, Reed and his colleagues at Monell published a study, which has yet to be published in a scientific journal, describing a rapid odor test that could screen for Covid-19.

In contrast, only a minority of people with Covid-19 end up increasing the temperature. Fevers also tend to be fleeting, while anosmia can persist for several days.

An odor test could also come with an attractive price tag, perhaps as low as $ 0.50 (€ 0.41) per card, said Derek Toomre, cell biologist at Yale University and author of the Larremore document. Toomre hopes his version will fit. The test, the U-Smell-It test, is a small assortment of scratch and sniff scents laid out on paper charts. People taking the test choose scent wells, inhale, and guess in a smartphone app, pulling to correctly guess at least three of the five scents. Different cards contain different scent combinations, so there is no answer to memorize.

Toomre estimated that the test could be passed in less than a minute. It’s also a manufacturer’s dream, he said: a single printer “could produce 50 million of these tests per day.” Figures like this, he argued, could make a huge dent in a country hampered by a widespread lack of access to tests that directly look for pieces of the coronavirus.

In many cases of Covid-19, the loss of odor can persist long after the virus is gone and people are no longer contagious – a complication that could put some people in post-Covid purgatory

In their study, Larremore, Toomre, and their collaborator Roy Parker, a biochemist at the University of Colorado, Boulder, modeled such a scenario using computer tools. Administered daily or almost daily, an odor shield that detected at least 50 percent of new infections was able to cancel outbreaks almost as well as a more accurate, slower lab test administered once per week.

Such tests, Larremore said, could function as an entry point screen on college campuses or in offices, perhaps in combination with a rapid viral test. There might even be a place for them at home, if researchers can find a way to minimize the abuse.

“I think it’s perfect,” said Dr. Carol Yan, ear, nose, and throat specialist at the University of California, San Diego. “Testing people over and over will be a valuable part of it.”

Toomre is seeking emergency use authorization for U-Smell-It from the United States Food and Drug Administration, and has partnered with a number of groups in Europe and elsewhere to test it in actual conditions.

However, translating theory into practice will pose many challenges. Smell tests that can reliably identify people with coronavirus, while excluding people with something else, are not yet widely available. (Hopkins pointed to a few scent tests, developed before the pandemic, which cost around $ 30 [€25] If ever they were deployed in bulk, they would inevitably miss some infected people and, unlike tests that look for the real virus, could never diagnose the disease on their own.

And the loss of odor, like fever, is not exclusive to Covid-19. Other infections can dull a person’s sense of smell. The same goes for allergies, nasal congestion due to colds or just the aging process. About 80 percent of people over 75 have some degree of odor loss. Some people are born anosmic.

Additionally, in many cases of Covid-19, the loss of odor can persist long after the virus is gone and people are no longer contagious – a complication that could put some people into post-Covid purgatory if they have to. to rely on scent screens to resume activity, says Yan.

There are also many ways to design a scent based screen. Odors associated with foods popular in some countries but not in others, such as bubble gum or licorice, can skew test results for some people. People who grew up in very urban areas might not easily recognize smells from nature, such as pine or fresh cut grass.

Smell is also not a binary sense, strictly on or off. Reed advocated a step in which candidates assess the intensity of a test’s odors – a recognition that the coronavirus can significantly reduce smell but not eliminate it.

But the more complicated the test, the more difficult it will be to manufacture and deploy quickly. And no test, even a perfectly designed one, would work with 100% accuracy.

Dr Ameet Kini, a pathologist at Loyola University Medical Center, stressed that scent testing would not be free from problems associated with other types of testing, such as poor compliance or refusal to isolate.

Odor screens are “probably better than nothing,” Kini said. “But no test is going to stop the pandemic in its tracks unless it is combined with other measures.” – New York Times