Trained scent dogs detect air travelers with COVID-19
‘Sniffer dogs’ could use their highly developed sense of smell to identify people infected with COVID-19 whether or not they have symptoms, randomized triple-blind validation shows trial and actual sightings published yesterday in BMJ Global Health.
In the spring of 2020, a team led by researchers from the University of Helsinki trained four dogs by randomly presenting them with skin swabs from 420 parallel samples from 114 people infected with wild-type SARS-CoV-2 and 306 controls. negative over seven sessions. Each dog had been previously trained to detect illegal drugs, dangerous goods or cancer.
At Helsinki-Vantaa International Airport, dogs sniffed skin swabs from 303 incoming passengers also tested for COVID-19 by polymerase chain reaction (PCR) from September 2020 to April 2021.
Accuracy greater than 90%
Compared to PCR, dogs had an estimated accuracy in detecting SARS-CoV-2 of 92% (95% confidence interval [CI], 90% to 93%), a sensitivity of 92% (95% CI, 89% to 94%) and a specificity of 91% (95% CI, 89% to 93%). They were much less accurate in detecting infections caused by the Alpha variant (89% for wild-type virus versus 36% for Alpha; odds ratio [OR]14.0 [95% CI, 4.5 to 43.4]).
But this latest finding also illustrates how well dogs can distinguish between different smells, the team said. “This observation is remarkable because it proves the powerful discriminatory power of scent dogs,” they wrote.
“The obvious implication is that training samples should cover all epidemiologically relevant variants. Our preliminary observations suggest that dogs primed with one type of virus can within hours be retrained to detect its variants.”
Dogs correctly identified 296 of 300 samples (99%) identified as negative by PCR but incorrectly identified four positives as negative. Twenty-eight samples were from people with asymptomatic cases; only one of them was missed and two were not sniffed, for an accuracy rate of 89%.
In the airport setting, dog identifications matched those from PCR in 98.7% of COVID-negative swabs. A low prevalence of SARS-CoV-2 at the airport (0.47%) did not allow for sensitivity analysis, but ad hoc analysis using protein spike samples from 155 people who tested positive by PCR did estimated a total accuracy of 98% (95% CI, 97% to 99%).
Role in screening many people
The researchers observed only small variations in the dogs’ abilities, with the best performers reaching 93% for sensitivity and 95% for specificity, and the worst performing at 88% and 90%, respectively.
Based on these results, the team calculated the proportion of true positive and true negative results in two hypothetical scenarios reflecting the COVID-19 population prevalence of 40% and 1%.
In the 40% prevalence scenario, the true positive rate was estimated at 88%, with a true negative rate of 94.5%, indicating that the information provided by the dog increased the chance of detection to approximately 90%. . But for a prevalence of 1%, the true positive rate was estimated at just under 10%, while the true negative rate was nearly 100%.
Researchers said scent dogs could allow for more efficient screening of large numbers of people for SARS-CoV-2 in busy environments such as hospitals or ports, as well as detection of other pathogens during future pandemics.
Dogs can detect odors as low as one part per trillion, far beyond any available technology. Although the exact mechanisms of this ability are unknown, the researchers said dogs would detect volatile organic compounds released during different metabolic processes, including bacterial, viral and parasitic infections.