Could a Simple Smell Test Screen People for Covid-19?

A simple, scratch-and-sniff test could play a key role in curbing the spread of COVID-19, at a fraction of the cost of high-tech tests that are difficult to scale and take longer to return results, new CU Boulder research suggests.

“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?” said author Roy Parker, a professor of biochemistry and director of CU’s BioFrontiers Institute. “We were surprised by how good the results were.”

For the study, Parker and Dan Larremore, an assistant professor of computer science, teamed up with CU Boulder alumnus Derek Toomre, a professor at the Yale School of Medicine who has developed an index-card sized test that interacts with a smartphone app to assess sense of smell.

Studies show that, when simply asked about their symptoms, only about half of people with COVID-19 report loss of smell, or anosmia. But when given a standardized test, with no visual clues to alert them to what they’re smelling and a range of scents chosen to catch even faint loss of smell, that number rises to eight in 10, 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. Anosmia also lasts longer, affecting patients for a week or more while fever may only last a day or two.

While fever is associated with many diseases, loss of smell without a stuffy nose is highly specific to COVID-19, possibly due to the fact the virus tends to enter the body and replicate via ACE2 receptors, which are extremely abundant in cells in nasal passages believed to influence sense of smell.

“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?’” said Larremore.

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