The smell test

Something as simple as a 50-cent scratch-and-sniff could hold the keys to stemming the spread of the coronavirus at a fraction of the cost and time of high-tech tests, 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?” author Roy Parker, a professor of biochemistry at CU said. “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 alumnus Derek Toomre, a professor at the Yale School of Medicine who has developed a call phone app test that assesses sense of smell.

Studies show that, when simply asked about their symptoms, only about half of people with COVID-19 report loss of smell, aka anosmia. But when given a standardized test, 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. In addition, while fever is associated with many diseases, loss of smell without a stuffy nose is highly specific to COVID.

The team used modeling to predict the effect of smell-testing in several hypothetical scenarios, including: on a college campus where individuals were tested once a week, every three days or daily; and at a one-day event where it was used for point-of-entry screening.

In each case, the sniff-test served not as a definitive diagnostic test, but as a screening tool. Those who failed would then be referred for a gold-standard PCR or a rapid antigen test. In general, it was found that scratch-and-sniffs every three days worked better than weekly PCR tests in curbing infection at a tiny fraction of the price.

“We found that you could reduce risk inside by 75 percent if you tested everybody, and it would only cost about 50 cents each,” Parker said.

Although the test is not commercially available yet, the team has applied for Emergency Use Authorization from the FDA. If approved, they could swiftly ramp up production to hundreds of millions of tests per week.

The findings have not yet been published in a peer-reviewed journal, and the authors caution that more research is necessary, but they are optimistic. “This is not a silver bullet,” said Larremore. “But it could be another useful tool in our repertoire."