I’ve written before about COVID-19 scent-detection dogs. I get lots of questions about them, and there are now several groups working in this area. There’s been a mix of information to date, ranging from encouraging to some pretty bad preliminary studies released on pre-print websites and other places. A dog’s nose is a wonderful thing (except when my dog sticks his in places I don’t want it to go), and dogs have been shown to be able to detect a wide range of different scents with great sensitivity.

The first question is: Will dogs be able to detect people with COVID-19?

If the answer is yes, then the bigger question is, will it be a practical way to detect people with COVID-19?

We may get more answers now that dogs are being used in a Finnish airport to sniff out COVID-19.  Ten dogs have been trained to detect people with COVID-19 based on smelling wipes collected from individuals. News reports include claims of close to 100% accuracy… I’d love to see good data on that, as I suspect it’s not 100% effective in the field. However, even if the dogs are moderately effective, they could be a useful tool when combined with other measures (e.g. rapid confirmatory testing of people that dogs flag as potentially infected).

My big questions at this point is, how effective is it really?

• We need to consider both sensitivity (how good dogs are at detecting infected people) and specificity (how good they are at only detecting infected people).
• For a screening test, we want a test that is highly sensitive, meaning it detects most infected people, even if it has some false positives (i.e. people who are mistakenly identified as positive but aren’t actually infected). That works if the false positive rate isn’t massive and if there is a convenient way to follow up to confirm who’s really positive. If we have a quick follow up test of another kind, the initial false positives are a bit of a hassle but not a big deal and easy enough to weed out, so we could tolerate some loss of specificity.
• False negatives on the other hand (i.e. people who are infected but go undetected by the test) are a bigger concern.
• So, knowing the sensitivity and specificity of these COVID019 detection dogs in a field situation (where there are lots of people of different types, with different stages of infection and with different smells) is key. Hopefully that’s being studied well.

Another question I have is, what’s the management plan for dogs that stick their noses in wipes from people with COVID-19?

• Dogs have limited susceptibility to SARS-CoV-2, but limited and zero aren’t the same.
• Will the dogs be screened in case they get infected in the process?
• And (an oddball question perhaps) if a dog gets infected, does it lose the ability to detect infection in people? would the dog then smell the scent associated with the virus all the time?

There will be more to come, I assume.