Can sniffer dogs really detect COVID almost as well as a PCR test? It turns out they can
Dogs have an extraordinary sense of smell. We use this ability in many ways, including training them to find illegal drugs, dangerous goods, and even people.
In recent years, the dog’s sense of smell has also been used in the medical field. These remarkable animals can be trained to detect cancer, diabetes and – most importantly – epileptic seizures before they occur.
At the beginning of the pandemic, the possibility of using dogs to detect COVID was explored in some countries. And while the results of these early attempts exceeded most people’s expectations, many questions remained unanswered. These included how well those results would stand up to more rigorous scientific scrutiny and how well dogs would behave outside of the research lab’s artificial environment.
Read more: Yes, dogs can sniff out COVID. But not after dinner when they need a nap
Last week, we got closer to answering these questions with an article published in BMJ Global Health, which found that dogs can detect COVID almost as well as PCR tests in certain circumstances.
What did the researchers test?
This article reported the results of two studies. In both studies, four dogs were tested to see how well they detect COVID (according to the gold standard test, PCR) from skin swabs from people with or without COVID.
These dogs didn’t just come off the street; They already had considerable training in detecting drugs, dangerous goods or cancer.
Read more: The Smell of Disease: 5 Questions Answered About Using Dogs — and Mice and Ferrets — to Detect Disease
The first study
In the first study, the researchers looked at whether the dogs could identify COVID in the skin swabs of 420 volunteers, 114 of whom had tested positive for COVID by PCR.
The study was rigorous, with several safeguards against compromising the results. This involved an elaborate study protocol involving a number of separate assistants and a handler. Neither of them knew if the sample came from someone with COVID, so they couldn’t intentionally or unintentionally influence the result.
The dogs detected COVID with a sensitivity of 92% (which refers to their ability to correctly identify those with infection) and a specificity of 91% (their ability to correctly identify those without infection).
Although there were some differences between the dogs, they all performed exceptionally well. No major disclaimers here, this was a great result.
The second study
The second study was important because its goal was to see how well the dogs could hold their own in the clutter of the real world. In this real-world experiment, dogs sniffed 303 arriving passengers at Helsinki-Vantaa International Airport in Finland. Each passenger also took a PCR test.
The dogs agreed with the PCR results in 296 of 303 (98%) specimens and correctly identified swabs as negative in 296 of 300 (99%) specimens.
The important consideration when interpreting this result is that this happened during airport security, a situation where you wouldn’t expect many people to test positive.
In this type of low-prevalence environment, you want dogs to be able to screen passengers with a high “negative predictive value”. That means you want the dogs to be able to identify people who don’t carry the virus to distinguish them from those who may carry it. Then you would do confirmatory PCR testing on that last group.
In an environment where the prevalence of COVID is around 1%, such as an airport, the researchers estimated the “negative predictive value” for dogs screened for COVID to be 99.9%. That means the dogs are expected to correctly rule out 99.9% of passengers as having COVID. This is another fantastic result.
Read more: Want to reduce your chance of catching COVID on an airplane? Wear a mask and avoid business class
Low tech and instant
In a world where we rely on expensive technological solutions, finding a low-tech option for COVID screening is reassuring.
Importantly, however, the study highlights that dogs can be quickly trained for the task and are ideal for screening in high-throughput environments such as airports because they are accurate and provide instant results.
While nothing should surprise us about our closest friend, another incredible finding from this study was the suggestion that the dogs may have been able to discriminate between variants of SARS-CoV-2, the virus that causes COVID.
While other possible explanations cannot be ruled out, the dogs’ performance appeared to decline with the advent of the alpha variant. This was attributed to the dogs being able to tell a difference between this variant and the wild-type virus they were originally trained on.
These studies confirm that nothing could be further from the truth when we say that you can’t teach an old dog new tricks.
Read more: Why are there so many new Omicron subvariants like BA.4 and BA.5? Will I get infected again? Does the virus mutate faster?