Trained dogs can identify COVID-19 by sniffing skin swabs, study says

Even when taken into a real-world setting — an airport — the dogs were able to correctly identify passengers as negative for COVID-19 almost every time.

"Scent dogs can provide an invaluable tool for limiting viral spread during a pandemic, serving for example at air and seaports,” Anu Kantele, professor of infectious diseases and chief physician at the University of Helsinki and Helsinki University Hospital, said in a press release. “Such a reliable, cheap approach to rapidly screen a vast number of samples or to identify passing virus carriers from a large crowd is of value particularly when the testing capacity with traditional approaches is insufficient.”

Scent detection dogs have been trained to use their sense of smell to identify and locate substances or people.

Since the start of the pandemic, numerous researchers and organizations have theorized that dogs might be able to assist in identifying COVID-19 cases fast by utilizing their superior sense of smell. Several institutions even began to train dogs to identify the scent of the virus.

But few studies have tested this ability out in a real-world setting.

In this new study, researchers wanted to do just that by first training a set of dogs to identify samples of COVID-19, then testing their skills in a laboratory setting before finally presenting them the final test: bringing the dogs to an airport to screen passengers.

The four dogs trained for this study — three Labrador retrievers named Silja, Rele and Kosti, and one white Shepherd named E.T. — all had previous experience with scent work.

They were trained using samples provided by inpatients and outpatients who had been recruited from Helsinki University Hospital.

A skin sample meant a strip of gauze that volunteers had swabbed on their neck, throat area, forehead and wrists.

Once the dogs showed they could recognize the scent of a positive COVID-19 case, researchers introduced samples of patients who had compounding factors such as asthma, cancer or diabetes to see if the dogs would still be able to tell who had COVID-19 or not, even with these competing elements.

To indicate a positive test, the dogs would show their handler a signal that had been decided upon during the training. One dog would paw in the direction of the positive sample, another would freeze and put her paw to her nose after sniffing a positive sample, and the other two were trained to sit to signal a positive sample.

In the second stage, the dogs’ ability was tested in a laboratory setting.

Researchers designed a study in which neither the dog, dog handler or the researcher presenting the swabs for sniffing would have any idea which of the samples were positive cases and which were negative, in order to cut down on the possibility of bias.

The dogs sniffed an identical set of samples to allow comparisons between dogs.

In this phase, the dogs sniffed 420 samples in total — 114 COVID-19 patient samples confirmed by PCR tests and 306 control samples from healthy individuals.

The dogs were able to recognize whether a sample was positive or negative correctly 92 per cent of the time.

The final leg of the experiment was run at Finland’s Helsinki-Vantass International Airport. At the airport, a specifically designed cubicle was installed at the arrivals terminal to replicate the cubicle setting that the dogs had been trained on and gotten used to.

Between September 2020 and the end of April 2021, more than 10,000 travelers and airport employees took part in the experiment, 48 of which were judged to be positive for COVID-19 by the dogs.

Out of this large sample size, 303 travelers or airport employees agreed to take part in the validation portion of the experiment and take a PCR test as well as provide a skin swab for the dogs to sniff.

Using the data from the 303 people, the dogs were found to be 98.7 per cent accurate in identifying whether a sample was negative for COVID-19.

One limitation is that the number of people who tested positive by PCR in the airport experiment was so small that researchers couldn’t come to a clear picture of the dogs’ accuracy in terms of positive cases. However, the dogs were presented with samples known to be positive throughout the airport experiment as a way of keeping them familiarized with the scent they were searching for, and researchers said that the dogs’ proficiency in recognizing those samples was quite high.

Taken altogether, the research seems to indicate that dogs can be easily trained to identify COVID-19 with a high level of accuracy — something that could be helpful in situations where understanding the positive or negative status of a person quickly is imperative.

"Our research group will continue to study how scent dogs can best help our society. We hope that this newly published study will help to allocate funds for the development of this new ‘tool’,” Anna Hielm-Björkman, leader of the DogRisk research group and one of the authors of the study, said in the release. “There are many other diseases where research could benefit from the excellent sense of smell that these dogs possess.”

Researchers pointed out that even when the dogs struggled, it highlighted their highly discerning abilities.

“I was particularly impressed by the fact that dogs performed worse with samples we had collected from patients suffering from a disease caused by a coronavirus variant,” Kantele said. “The explanation is simple: the dogs had originally been trained with the initial wild-type virus, and thus they did not always identify the variant samples as positive. This reveals their incredible ability of discrimination.”