Can 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 – with absolute accuracy, which could instantly determine who is virus-free and safe to accept, and who, positively infected, should be rejected.

That reality does not exist. But while many countries are struggling to regain the semblance of normal life amid the uncontrolled spread of the virus, some scientists think a quick test consisting of something more than a stinking strip of paper could at least bring us closer.

The test does not look for the virus itself, nor can it diagnose the disease. Instead, it depicts one of Covid-19’s trademarks: loss of sense of smell. Since last spring, many researchers have recognized the symptom, also known as anosmia, as one of the best indicators of persistent coronavirus infection, capable of identifying even people who do not otherwise feel ill.

An odor test cannot mark people who become infected with the coronavirus and never develop any symptoms at all. But in a study not yet published in a scientific journal, a mathematical model showed that snout-based tests, if applied widely and often enough, could detect enough cases to greatly reduce transmission.

Odor tests could function as an entry point on campus or in offices, perhaps in combination with a rapid virus test

Daniel Larremore, a public health researcher at the University of Colorado, Boulder, and lead author of the study, stressed that the work of his team was still purely theoretical. Although some odor tests are already used in clinical and research facilities, the products are expensive and laborious to use and are not widely available. And in the context of a pandemic, there is still no real-world data to support the effectiveness of odor tests as a frequent screen for coronavirus. Given the many troubles that have so far hampered pandemic efforts, some experts doubt that odor tests could be distributed widely enough or made fraudulent enough to reduce the spread of the infection.

“From the beginning, I was intimately involved in efforts to recognize the loss of odor as a symptom of Covid,” said Dr. Claire Hopkins, an ear, nose and throat surgeon at Guy’s and St Thomas’s hospitals in the UK and author of a recent commentary on the subject in The Lancet. “But I just don’t see any value as a screening test.”

A reliable odor test offers many potential benefits. It could capture many more cases than fever checks, which mostly floated as tools for checking Covid-19. Studies have found that about 50 to 90 percent of people who test positive for coronavirus experience some degree of measurable odor loss as a result of smoking the virus when it attacks cells in the airways.

“It’s really like the function of the virus that’s in the nose right now,” said Danielle Reed, assistant director of the Monell Center for Chemical Senses in Philadelphia. “It complements so much information you get on other tests.” Last month, Reed and her colleagues at Monell published a study, not yet published in a scientific journal, describing a rapid odor test that might be able to review Covid-19.

In contrast, only a minority of people with Covid-19 eventually raise their temperature. Fever is also transient, while anosmia can last for many days.

The odor test could also come with an attractively low price, maybe as much as $ 0.50 ($ 0.41) per card, said Derek Toomre, a cell biologist at Yale University and author of Larremore’s paper. Toomre hopes his version will fit the bill. The test, the U-Smell-It test, is a small smorgasbord of the smell of scratches and sniffing arranged on paper cards. People being tested select sources of odors, inhale and tap into a smartphone app, firing to correctly hit at least three of the five odors. Different cards contain different combinations of scents, so there is no key to the answer that is remembered.

Toomre estimated that the test could be done in less than a minute. It’s also a manufacturer’s dream, he said: One printer “could produce 50 million of these tests a day.” Such numbers, he argued, could create a huge hole in the country hampered by a widespread lack of access to tests that directly look for parts of the coronavirus.

In many cases, Covid-19 odor loss can last long after the virus disappears and people are no longer contagious – a complication that could take some people to purgatory after Covid

In their study of Larremore, Toomre and their collaborator Roy Parker, a biochemist at the University of Colorado at Boulder, modeled such a scenario using computational tools. Applied daily or almost daily, the odor screen that caught at least 50 percent of new infections managed to eliminate disease outbreaks almost as well as a more accurate, slower lab test given only once a week.

Such tests, Larremore said, could function as an entry point on campuses or in offices, perhaps in combination with a rapid virus test. They could also have a place in the house, if researchers find a way to minimize abuse.

“I think this is the place,” said Dr. Carol Yan, an ear, nose and throat specialist from the University of California, San Diego. “Repeated testing of people will be a valuable part of this.”

Toomre is seeking emergency approval for U-Smell-It from the U.S. Food and Drug Administration, and has teamed up with a number of groups in Europe and elsewhere to test it in real-world conditions.

Putting theory into practice, however, will lead to many challenges. Odor tests that can reliably identify people who have coronavirus, and exclude people who are ill with something else, are not yet widely available. (Hopkins pointed to several odor tests, developed before the pandemic, that cost about $ 30 [€25] each and remain in limited quantities.) If they were ever unpacked in bulk, they would inevitably miss some infected people and, unlike tests that look for the actual virus, would never be able to diagnose the disease on their own.

A coronavirus testing site in Los Angeles. Odor tests, unlike PCR and antigen tests, would not diagnose the disease or directly look for the virus. Photo: Kendrick Brinson / The New York Times

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

Moreover, in many cases, Covid-19 odor loss can last long after the virus disappears and people are no longer contagious – a complication that could take some people to purgatory after Covid if they are forced to rely on scented screens to continue activity, Yan said.

There are also many ways to design a scent-based screen. Food-related odors that are popular in some countries but not in others, such as chewing gum or licorice, could skew test results for some individuals. People who grew up in an urban environment may not recognize scents from nature, such as pine or freshly cut grass.

Smell is also not a binary feeling, strictly on or off. Reed advocated a step in which test takers assess the intensity of the test odor – acknowledging that the coronavirus can drastically reduce the sense of smell, but not eliminate it.

But the more complex the test, the harder it would be to produce and develop quickly. And no test, not even a perfectly designed one, would work with 100 percent accuracy.

Dr. Ameet Kini, a pathologist at Loyola University Medical Center, stressed that odor tests will not be free of problems associated with other types of tests, such as poor compliance or refusal of isolation.

Odor screens are “probably better than nothing,” he told China. “But no test will stop the pandemic if it is not combined with other measures.” – New York Times