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Study finds scent dogs accurately identify patients infected with COVID-19

A study found that screening by scent dogs at airports had a similar accuracy to PCR testing for the identification of patients with COVID-19

Using scent dogs for pre-screening at an airport has been found to be as accurate as PCR tests for the identification of patients infected with COVID-19. This was the conclusion of a study by a team of Finnish researchers.

Testing for the presence of COVID-19 has largely relied upon methods based on either a polymerase chain reaction (PCR) or lateral flow tests for specific antigens. PCR tests are sufficiently accurate so that if someone has a positive result, there is a 98% probability that they have COVID-19. Although less sensitive, antigen tests have a pooled sensitivity of 79% but a pooled specificity of 100%. Another potential form of testing involves the use of scent dogs and a 2016 study, it was shown that these dogs were able to differentiate between infected and non-infected cultured cells with bovine viral diarrhoea virus. The value of using dogs is that the animals have an extremely sensitive olfactory system with a lower limit of detection of one part per trillion.

During the pandemic, several small scale studies have already demonstrated how scent dogs can detect COVID-19 in different body fluids and while these results have been encouraging, real-world data are needed to confirm the value of scent dogs, particularly in situations where rapid detection is needed, for example, screening of patients arriving at an airport.

In the present study, the Finnish team compared the accuracy of scent dogs to detect COVID-19 in people arriving at an airport with standard PCR tests. The dogs were initially trained to identify the COVID-19 scent and then this process was validated by randomly presenting each of the dogs with positive and negative samples over a period of a few days. In the final and real-world part of the study, the scent dogs screened skin swab samples from incoming passengers at an airport and for whom, PCR tests were also performed. The main outcomes of interest were diagnostic accuracy (based on sensitivity, specificity and positive predictive value) and which were compared against the PCR test result.

Scent dogs and detection of COVID-19

A total of 4 dogs were used in the study and during the validation part, the dogs had an overall accuracy of 92% with a sensitivity of 92% and specificity of 91% compared to PCR test results.

For the real-world aspect of the study, the results for scent dogs and PCR tests were correctly matched for 97.7% of samples. However, in the real-world sample, there were few individuals who were actually infected hence there was a very low (0.47%) positivity rate. As a result, the researchers included an additional 155 positive samples, of which, the dogs accurately indicated 98.7% of these as positive.

The authors concluded that while the validation part of the study was successful, the lack of positive samples in the real-world part made it difficult to confirm the sensitivity for detection though use of additional samples did offer evidence of convincing accuracy.

Kantele A et al. Scent dogs in detection of COVID-19: triple-blinded randomised trial and operational real-life screening in airport setting BMJ Glob Health 2022

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