As soon as the pandemic kicked off in early 2020 researchers started looking at whether dogs could be used to sniff out patients with COVID-19. Now, a new study published in the journal BMJ Global Health, has reported on a robust, real-world investigation into this novel method of viral detection, finding it is potentially effective, at least in detecting COVID-negative people.
Despite only patchy evidence from studies in laboratory settings, COVID-sniffing dogs were commercially deployed within months of SARS-CoV-2 emerging. Reports have emerged of bands such as Metallica using the animals backstage to maintain bubbles of protection, constantly on the lookout for infected individuals.
This new research reports on a long real-world test investigating the accuracy of COVID-sniffing dogs at an airport. The airport experiment spanned six months, across the end of 2020 and into 2021.
Out of 303 passengers tested in the study the dogs matched PCR results 98 percent of the time. Certainly an impressive result, however, only three of the 303 cases were found to be PCR positive to SARS-CoV-2, and the dogs missed all three of those cases.
Follow-up PCR testing on those three positive cases found only one of the cases was a true infectious positive, while the other two were either false negatives or in a post-infectious period. So really, only one of the 303 cases in the airport study was a true symptomatic positive, and they were missed by the COVID-sniffing dogs.
However, the researchers did consistently present the dogs with COVID-positive samples across the course of the study in order to maintain their skills. The dogs effectively detected 155 of these COVID-positive samples across the course of study.
What this means is the researchers are generally confident the dogs have a high accuracy in detecting COVID-negative people. However, because of the low prevalence of COVID-positive cases in the study the researchers were unable to assess the dogs’ ability to catch those with SARS-CoV-2 infections.
“In our real-life setting with a very low prevalence, the performance in identifying negative samples was very good (98.7 percent),” the researchers write in the study. “Unfortunately, because of a low number of confirmed positive cases, accuracy with respect to positive samples could not be reliably assessed. However, ad hoc analysis also calculating the positive spike swabs showed a real-life performance of 98.5 percent for detecting positive samples.”
One interesting side note in the study is that the PCR-positive infectious case the dogs missed turned out to be a case with the Alpha variant of SARS-CoV-2. The researchers note the dogs were trained to detect the original type of the coronavirus. It may be possible that scent-profiles of subsequent emerging variants are different to the original SARS-CoV-2, meaning the dogs need to be retrained to target whatever viral variant is circulating at any given moment.
Ultimately, the study is a reminder there can be quite a gap between testing a dog’s sniffing ability in laboratory settings and translating that into a real-world environment such as an airport. In this case the study reported that in lab settings these dogs were 90 percent effective at distinguishing COVID-positive and -negative samples, but in real-world situations with a low-prevalence of cases the animals may be less accurate.
The researchers indicate their findings highlight the potential need to constantly retrain dogs to target specific viral variants. Plus, these dogs may be of use when large-scale rapid screening of big crowds is required and other rapid forms of testing are insufficient or unavailable.
The new study was published in the journal BMJ Global Health.
Source: University of Helsinki
