Scent dog identification of samples from COVID-19 patients – a pilot study | BMC Infectious Diseases | Full Text – Research article, Open Access – July 2020
With our search for solutions to the current health crisis focused only on cutting edge science, we sometimes forget to reevaluate older, simpler remedies that could be repurposed or improved quickly to use while we wait for a better technological solution.
As the COVID-19 pandemic continues to spread, early, ideally real-time, identification of SARS-CoV-2 infected individuals is pivotal in interrupting infection chains.
Volatile organic compounds produced during respiratory infections can cause specific scent imprints, which can be detected by trained dogs with a high rate of precision.
Eight detection dogs were trained for 1 week to detect saliva or tracheobronchial secretions of SARS-CoV-2 infected patients in a randomised, double-blinded and controlled study.
The dogs were able to discriminate between samples of infected (positive) and non-infected (negative) individuals with average
- diagnostic sensitivity of 82.63% (95% confidence interval [CI]: 82.02–83.24%) and
- specificity of 96.35% (95% CI: 96.31–96.39%).
During the presentation of 1012 randomised samples, the dogs achieved an overall average detection rate of 94% (±3.4%) with
- 157 correct indications of positive,
- 792 correct rejections of negative,
- 33 incorrect indications of negative or incorrect rejections of 30 positive sample presentations.
These preliminary findings indicate that trained detection dogs can identify respiratory secretion samples from hospitalised and clinically diseased SARS-CoV-2 infected individuals by discriminating between samples from SARS-CoV-2 infected patients and negative controls. This data may form the basis for the reliable screening method of SARS-CoV-2 infected people.
Abstract above – annotations from full-text article below:
Several studies have proven the canines’ extraordinary olfactory acuity to detect persons with infectious and non-infectious diseases like different types of cancer, malaria, bacterial, and viral infections, with usually high rates of sensitivity and specificity.
This is actually very important to understand for any kind of medical test results:
Sensitivity and specificity are statistical measures of the performance of a binary classification test, also known in statistics as a classification function, that are widely used in medicine:
Sensitivity (also called the true positive rate) measures the proportion of actual positives that are correctly identified as such (e.g., the percentage of sick people who are correctly identified as having the condition)..
Specificity (also called the true negative rate) measures the proportion of actual negatives that are correctly identified as such (e.g., the percentage of healthy people who are correctly identified as not having the condition).
A highly sensitive test rarely overlooks an actual positive (for example, showing nothing wrong despite a problem existing);
A highly specific test rarely registers a positive classification for anything that is not the target of testing (for example, finding one bacterial species and mistaking it for another closely related one that is the true target).
A test that is both highly sensitive and highly specific rarely records either false positives or false negatives.
A pathogen-specific odour that can be detected by dogs may be composed of specific patterns of volatile organic compounds (VOCs). Compared to bacteria, viruses have no own metabolism, and therefore VOCs are released by infected body cells as a result of metabolic host processes.
As dogs can be trained quickly, the aim of the present study was to test the concept of using dogs reliably and in real-time to discriminate between samples of SARS-CoV-2 infected patients and non-infected controls.
This method could be employed in public areas such as airports, sport events, borders or other mass gatherings as an alternative or addition to laboratory testing, thus helping to prevent further spreading of the virus or further outbreaks.
It seems dogs could be extremely useful in public areas. They are far less intimidating that healthcare workers in full “bunny suits” or any kind of police presence. A handler could just roam through a crowd and let the dog identify sick folks.
Of course, what should be done after such a person has been identified is a thorny question, since there have been armed resistance to some other efforts to enforce public health measures.
Saliva samples and tracheobronchial secretion samples were collected from hospitalised COVID-19 patients that showed clinical symptoms and were diagnosed as SARS-CoV-2 positive using nasopharyngeal swab samples. Negative control samples were obtained from SARS-CoV-2 RT-PCR negative people with no previous history of COVID-19.
For the dog training, a volume of 100 μl per sample was pipetted onto a cotton pad, which was placed into a 4 ml glass tube.
Dog training and study design
The presentation of the samples to the dogs was conducted via a device called Detection Dog Training System (DDTS; Kynoscience UG, Germany), which can present samples in a randomised automated manner without trainer interference.
The dog, its handler and a person observing the study were blinded during the double-blinded study. All personnel stood behind the dog during the test runs to avoid distraction.
The device recorded automatically the number and time length of each nose dip into the scent holes and the location of the positive and negative samples.
After a 2 weeks habituation process to the DDTS, the eight dogs needed 5 days of training in total until the detection rate was above chance.
This means that you can take any dog that’s familiar with the training device and train them to detect this particular virus in less time than it takes to get a test result these days (currently 8-10 or even 16 days).
While the dogs had only achieved an average detection rate of 50% on the second day of training, the values increased to 70% on day five and even 81% on day seven indicating a successful generalisation process.
Within randomised and automated 1012 sample presentations, dogs achieved an overall average detection rate of 94% (±3.4%) with 157 correct indications of positive, 792 correct rejections of negative, 33 false positive and 30 false negative indications.
The canines discriminated between infected and non-infected individuals with an overall diagnostic sensitivity of 82.63% (95% confidence interval [CI]: 82.02–83.24%) and specificity of 96.35% (95% CI: 96.31–96.39%). Sensitivity ranged from 67.9 to 95.2% and specificity from 92.4 to 98.9%
Timely and accurate detection of SARS-CoV-2 infected individuals is of uttermost importance for a society to control the pandemic. Our data indicate that detection dogs can be trained in just about a week to discriminate between samples of people infected and non-infected by SARS-CoV-2.
However, there was quite a range in variation of sensitivity for the individual dog and inbetween dogs. This can in part be explained with the dogs’ variable training background, signalment, personality traits and short training period of 7 days.
In comparison, the current gold standard diagnostic RT-PCR test of a nasopharyngeal swab can, in trained hands, have a false detection rate of 25% and a false positive rate of 2.3–6.9%
Detection dogs were able to discriminate respiratory secretions of infected SARS-CoV-2 individuals from those of healthy controls with high rates of sensitivity and specificity.
The current pilot study had major limitations which needs to be elucidated in future studies.
SARS-CoV-2 detection dogs may then provide an effective and reliable infection detection technology in various settings like public facilities and function as an alternative or addition to regular RT-PCR screening.
In countries with limited access to diagnostic tests, detection dogs could then have the potential to be used for mass detection of infected people. Further work is necessary to better understand the potential and limitation of using scent dogs for the detection of viral respiratory diseases.
Here’s my business idea: buy one of those scent training devices and offer to train people’s dogs to detect the coronavirus. Or, procure dogs that are good at this kind of job involving scent discrimination and training, get them trained, and then lease them out to folks who are attending events like concerts or even going into classrooms.
If a person had one of these dogs with them all the time, they’d be warned if people near them had the virus and could thus avoid them.
If my EDS disability didn’t prevent me from doing this kind of work with animals, which requires full concentration, physical manipulation, and immediate responses to animal’s slightest gestures, I would be doing this myself.
Though I was a professional dog trainer for a while, leaning over the animals would provoke my back pain which would then break my total focus on the animal.
It’s impossible to train an animal when pain is serious enough to disrupt not just my actions but also my thinking, especially since animals pick up the “vibe” of a wounded person and react with less trust.
The datasets used and/or analysed during the current study are available at Jendrny, Paula, Twele, Friederike, Schulz, Claudia, Meller, Sebastian, von Köckritz-Blickwede, Maren, Volk, Holger Andreas. (2020). SARS-CoV-2 detection dogs -a pilot study [Data set]. Zenodo. https://doi.org/10.5281/zenodo.3950074