COVID: dogs again better than cats, this time as virus sniffers

Another article showed the clear superiority of dogs over cats, this time for detection of SARS-CoV-2 virus (see covid dog sniffers BMCinfdis2020 in dropbox, or https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-020-05281-3 ). as per usual for these types of studies, Jon Pincus brought this to my attention.

 

Details:

--8 detection dogs were trained for 1 week to detect saliva or tracheobronchial secretions from Covid-19 patients in a double-blind randomized controled trial (though I’m not sure how they got the dogs to wear blind-folds…)

--saliva and tracheobronchial secretion samples were taken from seven hospitalized Covid-19 patients who had positive PCR tests for SARS-COV-2, and seven healthy adults

-- 2 of the positive samples were from  tracheobronchial secretions and the rest from saliva

 

Results:

--of the 1012 samples, overall average detection rate was 94% (+/- 3%):

    --positive results: correct for 157 samples, wrong for 30

    --negative results: correct or 792 samples, wrong for 33

    --sensitivity 82.63% (82.02-83.24%); specificity 96.35% (96.31-96.39%)

--no notable difference in detection ability between the saliva and tracheal secretions

 

Commentary:

--the impressive part of the study is that dogs can be trained in 7 days to detect the SARS-CoV-2 virus pretty accurately. There was variability here between dogs, with one having specificity of 97% and sensitivity of 95%

--another pre-publication study of 51 patients with or without SARS-CoV-2 found that spectrometry of breath samples could correctly classify 98% of patients, by assessing volatile organic compounds (VOCs) released by the metabolism of the virus or the host (see https://www.medrxiv.org/content/10.1101/2020.06.30.20143347v1.full.pdf). And the spectrometry was different for SARS-CoV-2 vs Influenza A

--though there really was no mention of cats in this article, and my title for the blog is truly (and unabashedly) misleading, it does turn out that dogs are indeed better than cats in that cats (but not dogs) have been shown to transmit SARS-CoV-2 (at least to other cats), see http://gmodestmedblogs.blogspot.com/2020/04/covid-dogs-are-clearly-better-than-cats.html. dogs may be able to harbor the virus, but no clear indication that they can transmit the virus to other animals or humans (see https://www.nature.com/articles/s41586-020-2334-5 )

--one issue here is what is the gold standard?? To classify patients as having Covid-19, studies tend to use the PCR and/or a typical symptom course for Covid-19 in a high prevalence area (and several studies of symptomatic Covid-19 patients do include on the order of 10-20% having negative PCRs but consistent symptoms/signs). PCR is not so accurate, with accuracy depending on the specific day after infection or start of symptoms, though 20% false negative rates were about the best found (eg see https://www.medrxiv.org/content/10.1101/2020.04.26.20080911v2.full.pdf or http://gmodestmedblogs.blogspot.com/2020/05/covid-false-negative-pcr-results-over.html). and, the false positive rate for PCR is about 3% or so...

--the researchers also note that older studies have shown that dog-sniffing does seem to accurately detect lung or breast cancers, malaria parasites, C difficile infections. these studies adds to the likelihood that this might be a useful technique fro SARS-CoV-2

 

Limitations of the study:

--there was significant variability between the dogs’ performances (much more so for sensitivity vs specificity), though the researchers feel that was related to the short training period, dog personality traits, and their training background.  In future studies these variables could be tested and specific dogs selected who were more accurate

--they did not look at other viruses with the dogs. It was intriguing in the other study mentioned above that the volatile organic compounds released by SARS-CoV-2 were different from Influenza A, but could the dogs be trained to distinguish these?  what about other viruses? What about the 2 common coronaviruses that recur regularly and cause the common cold?

--is there a difference in SARS-CoV-2 detection by the patient’s age, whether they are symptomatic vs asymptomatic vs presymptomatic, or by severity of symptoms?

--what about patients who harbor the SARS-CoV-2 virus but have a false negative PCR test? do they have suffiecient or necessary VOCs to allow dogs to distinguish them?

 

So, pretty interesting stuff, and should be looked at more rigorously in multiple settings, especially in light of the current (and likely future) surges in Covid-19 cases:

--there really is an urgent need for a very rapid, sensitive test SARS-CoV-2 test that is easily available. If dog-sniffing withstood the challenge of bigger and better studies, it might be great for screening passengers on airplanes, or people traversing state lines by car, or those going to college, or workplaces, or going to sports events, or living with vulnerable people, or …..  And get the results in seconds.

--even if the test is only moderately specific (ie, dogs cannot distinguish other coronaviruses from SARS-CoV-2), dog-sniffing might be a great way to sort people into the not-need-further-testing group from the need-a-better-test one, eliminating the need for more aggressive/expensive/time-consuming/delayed-results from the PCR tests we currently use

    --and, perhaps not so surprisingly, there are hospitals unconscionably  gouging the system for the cost of PCR testing, with the NY Times today reporting a bill for $1980 for a test, with other studies finding the cost is from $199 to $6408 at the same location (see https://www.nytimes.com/2020/08/03/upshot/nj-coronavirus-medical-bill.html )

--there is an inherent appeal to saliva testing (which was as good as tracheobronchial samples), much less uncomfortable, easier to do, and likely to be more acceptable to people

--perhaps most significantly, on watching a video of one of the dogs, it was clear that it was a black lab (a remarkably good choice, from my perspective. Happy to share astoundingly cute photos of my black lab from years ago) and confirming that it took only a matter of seconds to distinguish the positive samples

geoff

 

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