Scientists from the University of Helsinki found that trained sniffer dogs can accurately detect airport passengers infected with SARS-CoV-2, the virus responsible for COVID-19.
This method of detection is likely to be especially valuable, not only in the early stages of a pandemic when other resources might not yet be available, but also to help contain an ongoing pandemic.
The research is published in BMJ Global Health and was conducted by Anu Kantele et al.
Dogs have a very keen sense of smell and can pick up a scent at levels as low as one part per trillion, far exceeding any available mechanical techniques.
It is thought that they are able to detect distinct volatile organic compounds released during various metabolic processes in the body, including those generated by bacterial, viral, and parasitic infections.
In the study, researchers trained 4 dogs to sniff out SARS-CoV-2. Each of the dogs had previously been trained to sniff out illicit drugs or dangerous goods or cancer.
To test the dogs’ detection skills, 420 volunteers provided four skin swab samples each.
The 4 dogs each sniffed the skin samples from 114 of the volunteers who had tested positive for SARS-CoV-2 on a PCR swab test and from 306 who had tested negative.
The samples were randomly presented to each dog over 7 trial sessions.
Overall, the diagnostic accuracy of all samples sniffed was 92%: combined sensitivity— accuracy of detecting those with the infection—was 92% and combined specificity—accuracy of detecting those without the infection—was 91%.
Only minor variation was seen among the dogs: the best performance reached 93% for sensitivity and 95% for specificity; the worst reached 88% for sensitivity and 90% for specificity.
Some 28 of the positive samples came from people who had had no symptoms.
Only one was incorrectly identified as negative and two weren’t sniffed, meaning that 25 of the 28 (just over 89%) were correctly identified as positive: the lack of symptoms didn’t seem to affect the dogs’ performance.
The 4 dogs were then put to work sniffing out 303 incoming passengers at Helsinki-Vantaa International Airport, Finland, between September 2020 and April 2021. Each passenger also took a PCR swab test.
The PCR and sniffer results matched in 296 out of 303 (98%) of the real-life samples.
The dogs correctly identified the samples as negative in 296 out of 300 (99%) PCR negative swab tests and identified three PCR positive cases as negative.
After re-evaluation with clinical and serological data, one was judged to be SARS-CoV-2 negative, one SARS-CoV-2 positive, and one a likely post-infectious positive PCR test result.
Similarly, the dogs indicated 4 PCR negative cases as positive. These were all judged to be SARS-CoV-2 negative.
Because the prevalence of SARS-CoV-2 among the airport passengers was relatively low (less than 0.5%), 155 samples from people who had tested positive on a PCR swab test were also presented to the dogs.
The dogs correctly identified just under 99% of them as positive. Had these ‘spike’ samples been included in the real-life study, the dogs’ performance would have reached a sensitivity of 97% and a specificity of 99%.
The researchers acknowledge that dogs trained to sniff out other substances may mistakenly identify these substances as SARS-CoV-2 positive.
The required storage period of the training and spiked samples may also have affected the viability of the volatile organic compounds.
If you care about COVID, please read studies about universal antibody therapy for all COVID-19 variants, and this new oral drug may prevent death from COVID-19.
For more information about COVID, please see recent studies about people who get the highest and most durable protection from COVID vaccination, and results showing people with cancer do benefit from COVID-19 vaccination.
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