Scent dogs in detection of COVID-19: triple-blinded randomised trial and operational real-life screening in airport setting

Abstract

ObjectiveTo estimate scent dogs’ diagnostic accuracy in identification of people infected with SARS-CoV-2 in comparison with reverse transcriptase polymerase chain reaction (RT-PCR). We conducted a randomised triple-blinded validation trial, and a real-life study at the Helsinki-Vantaa International Airport, Finland.MethodsFour dogs were trained to detect COVID-19 using skin swabs from individuals tested for SARS-CoV-2 by RT-PCR. Our controlled triple-blinded validation study comprised four identical sets of 420 parallel samples (from 114 individuals tested positive and 306 negative by RT-PCR), randomly presented to each dog over seven trial sessions. In a real-life setting the dogs screened skin swabs from 303 incoming passengers all concomitantly examined by nasal swab SARS-CoV-2 RT-PCR. Our main outcomes were variables of diagnostic accuracy (sensitivity, specificity, positive predictive value, negative predictive value) for scent dog identification in comparison with RT-PCR.ResultsOur validation experiments had an overall accuracy of 92% (95% CI 90% to 93%), a sensitivity of 92% (95% CI 89% to 94%) and a specificity of 91% (95% CI 89% to 93%) compared with RT-PCR. For our dogs, trained using the wild-type virus, performance was less accurate for the alpha variant (89% for confirmed wild-type vs 36% for alpha variant, OR 14.0, 95% CI 4.5 to 43.4). In the real-life setting, scent detection and RT-PCR matched 98.7% of the negative swabs. Scant airport prevalence (0.47%) did not allow sensitivity testing; our only SARS-CoV-2 positive swab was not identified (alpha variant). However, ad hoc analysis including predefined positive spike samples showed a total accuracy of 98% (95% CI 97% to 99%).ConclusionsThis large randomised controlled triple-blinded validation study with a precalculated sample size conducted at an international airport showed that trained scent dogs screen airport passenger samples with high accuracy. One of our findings highlights the importance of continuous retraining as new variants emerge. Using scent dogs may present a valuable approach for high-throughput, rapid screening of large numbers of people.

Dogs can discriminate between human baseline and psychological stress condition odours

“…It must be noted that our sample consists of only four dogs. This sample size is, however, in-line with other bio-detection studies due to the time-consuming nature of training highly specialised dogs (e.g., Cornu et al [ 41 ]: one dog; Bomers et al [ 43 ]: one dog; Taverna et al [ 42 ]: two dogs; Murakra et al [ 40 ]: four dogs, Kantele et al [ 45 ]: four dogs). Importantly, as this is a proof of principle study, a small sample size does not compromise the findings, as the goal of the study is not to generalise the findings to all dogs, but rather to demonstrate that some, carefully selected and highly trained dogs can successfully discriminate between the samples.…”

“…It should be noted that this paradigm does not allow insight into a dog’s untrained response to an odour; however, it does offer a level of control that is desirable when attempting to address the question of whether a physiological process confers a detectable odour. Most large-scale human disease studies use a ‘generalisation paradigm’ whereby dogs are taught their target odour by being shown many samples taken from people who have the same health condition (e.g., [ 45 ]). Over repeated exposure, the aim is that dogs learn to recognise commonality associated with the condition across the samples and can ignore individual differences unrelated to the condition (e.g., age, sex, diet, medications).…”

Travel in the Time of COVID: A Review of International Travel Health in a Global Pandemic

“…Pre-departure rapid antigen testing compared to PCR in Vancouver demonstrated the feasibility of using lateral flow, rapid antigen tests in the airport pre-departure [26]. The use of specially trained dogs to identify individuals with asymptomatic or mild COVID-19 may provide an additional innovative approach to detect infected travelers at airports, train stations, and other ports of embarkation [70,71]. Pre-travel screening has been a frequently implemented strategy to reduce the risk of SARS-CoV-2 importation.…”

The dogs learning to sniff out disease

“…Also, having a small sample of an odour in a lab is very different from having a huge amount of odour coming from various sources out in the real world. Dogs can have a hard time picking people out as they stand in line or walk by, so a trial at an airport in Finland set up testing stations at which the dogs could sniff samples from people one by one 4 .…”