Could scratch-and-sniff tests help screen for COVID? New study tries to find out
Loss of smell is a symptom unique to the coronavirus. It manifests itself differently than the congested, runny nose-type anosmia typical of a common cold, and it can linger for more than a week in some people.
So, researchers from the University of Colorado Boulder put this sense to work by developing an index card-sized scratch-and-sniff test that could help spot coronavirus-infected individuals faster than a traditional PCR test, which can take days to provide diagnoses.
Not only is the test cheaper — ringing up to an estimated 50 cents apiece — but it could also serve as a better COVID-19 screening tool than temperature checks, which are being used today in an attempt to control outbreaks, according to a university news release.
The team’s study, which has not been peer-reviewed, was posted Dec. 2 on the pre-print service medRxiv.
“Given that we are already broadly screening for temperature at places like hospitals and airports, we asked: ‘What would happen if we started screening for loss of smell instead?’” study co-author Dan Larremore, an assistant professor of computer science at CU Boulder, said in the release. “This is not a silver bullet, but it could be another useful tool in our repertoire of tools for getting a handle on this virus.”
The test could be a more beneficial alternative to temperature checks because loss of smell typically lasts longer (one to two weeks, maybe even months) than a fever (one to two days). Also, most people don’t notice their smell is malfunctioning until tested.
When asked about their symptoms, only about 50% of people with coronavirus report no smell, the researchers said of past studies. But when given a standard smell test with a range of scents, that percentage jumps to 80%, “even among people with no other symptoms.”
“That’s far more prevalent than fever, which impacts fewer than one in four people with the virus,” the team said in the release.
The scratch-and-sniff test comes on a card with five different scents. During the test, a person has to enter their answers in an app on a smartphone, which then tells them if they passed.
If their answers didn’t match the provided scents, the app instructs the person to get a coronavirus PCR test to confirm infection.
The researchers used mathematical modeling to predict how well a smell test would work in catching infected individuals in different scenarios.
“A lot of people have joked about this idea, but this is the first effort to ask in a rigorous, mathematical way: Could screening for loss of smell actually work?” study co-author Roy Parker, a professor of biochemistry and director of CU’s BioFrontiers Institute, said in the release. “We were surprised by how good the results were.”
In a hypothetical college campus with 20,000 people — 50% or more of which have COVID-19 and no sense of smell — the researchers found that administering smell tests every day or every third day was enough to prevent major coronavirus outbreaks.
When 75% or more people had COVID-19 and no smell, tests conducted every third day were more effective than weekly PCR testing, assuming results came back the following day.
In other words, you can reduce risk by 75% if everyone completed a scratch-and-sniff exam, Parker said.
The only scenario in which weekly smell tests were able to “fully control outbreaks” was when 90% of people on the simulated college campus lost their smell from COVID-19, according to the study. Other than that, weekly tests “failed” at controlling outbreaks.
Smell test worth a fraction of PCR exam cost
To test 2 million people a day, PCR tests worth $50 each would cost $100 million, whereas a smell test worth an estimated 50 cents would cost $1 million.
“Moreover, since [smell] can be self-tested, there is no need for the logistics of sample collection and transport, which can further reduce costs,” the researchers said in their study.
“We hope that it would allow for a fast and easy test that anyone can take anywhere and can be applied to any place that is using temperature screening as an inexpensive way to help avoid shutdowns, keep businesses open and decrease the terrible human toll,” study co-author and CU Boulder alumnus Derek Toomre, now a professor at the Yale School of Medicine, said in the release.
Toomre sent an application to the U.S. Food and Drug Administration for an emergency use authorization for the scratch-and-sniff test in October, according to the release. If approved, he said they can produce “potentially hundreds of millions of tests per week.”
