Can Trained Dogs Make COVID Screening More Efficient?

In an unusual scene, school children lined up standing 6 feet apart and facing away from a couple yellow labs led by handlers. One by one, the dogs sniffed each student's ankles and feet. Sometimes, the dogs would sit down before moving onto the next person, indicating that COVID-19 was potentially detected.

In this California-based pilot program, screening by scent-trained medical alert dogs had a sensitivity of 83% (95% CI 75-90) and a specificity of 90% (95% CI 89-91), reported Carol Glaser, DVM, MD, of the California Department of Public Health, and colleagues in a research letter published in JAMA Pediatrics.

Glaser said that at the time they were designing the study, at-home tests weren't yet available and antigen testing in schools was time-intensive and used a lot of resources. She heard about reports from around the world on the potential of using dogs to detect COVID, which sparked an idea.

"Wouldn't it be cool if we could use dogs in the schools instead of, or in conjunction with, antigen tests?" Glaser posed.

For this pilot program, Early Alert Canines trained two yellow labs -- Rizzo and Scarlet -- to detect volatile organic compounds (VOCs) emitted by people with COVID. Dogs are commonly trained for other medical purposes, such as glucose monitoring.

Co-author Carol Edwards, executive director of Early Alert Canines, said they collected socks from people who tested positive and negative for COVID. They then trained the dogs to detect VOCs using a scent wheel.

"Once the dogs proved they could identify the positive samples on the scent wheel, we began to teach them to sniff human ankles and alert if they found the VOCs," Edwards explained. "The dogs did not show any difficulty as variants evolved, although we continue to collect socks and train in our facilities when we are not deployed. This ongoing training could be why the dogs have not had a difficult time with variants."

Glaser told MedPage Today that, in the lab, the dogs had 99% accuracy when sniffing out socks from people with COVID.

After the dogs were deemed up to snuff, it was time to deploy them to K-12 California schools that volunteered to be part of the pilot program. Two-thirds were public schools, and the rest were private schools. On the same day antigen testing was already scheduled, the kids lined up 6 feet apart so Rizzo and Scarlet could sniff each one. For privacy reasons, everyone faced away so they couldn't see either dog sit down if someone was sniffed out as potentially positive. Antigen tests were administered to check the dogs' accuracy.

"If a dog signaled positive and antigen testing results were negative, the signal was considered falsely positive; if a dog did not signal and antigen testing results were positive, the signal was considered falsely negative," Glaser and colleagues wrote in their research letter.

The program was conducted over 50 visits to 27 schools from April to May 2022. In total, 3,897 paired antigen-dog screenings were completed among 1,558 participants. Median age was 13, and 55.8% were female. Of the participants, 89% were students and 68% were screened at least twice.

The dogs had an overall accuracy of 90%, correctly identifying 85 COVID infections and ruling out 3,411 infections. They inaccurately signaled infection in 383 cases and missed 18 infections.

Other studies, including a large study in Germany, have explored similar questions. In most of this past research, the dogs have smelled samples in receptacles or individual people, which reduces outside distractions and increased accuracy. Glaser said her team wanted to explore a more practical application that would mimic how canine detection would be used in the real world.

They noted that the low levels of SARS-CoV-2 transmission during the study period and therefore the low number of COVID infections were limitations to the study.

"While modifications are needed before widespread implementation, this study supports use of dogs for efficient and noninvasive COVID-19 screening and could be used for other pathogens," Glaser and team concluded.

Now that COVID testing in schools is no longer common practice, Rizzo and Scarlet have turned their noses to detect COVID in California nursing homes.

Comment