Dogs can smell 'super bugs' helping to heal people

beagle sniffs deadly bacteriaWe have all heard about miracle diagnosis by dogs alerting owners to cancers and other illnesses they have in their bodies, but here is a 2012 study to objectify their ability.

The dog was tested with Clostridium difficile (C. difficile) which is a bacterium that is related to the bacterium that cause tetanus and botulism. Unchecked, both of these diseases can lead to death.

The C. difficile bacterium has two forms, an active, infectious form that lives short time out of a host, and a non-active, "non-infectious" form, called a spore. The downside is that the spore can live in the environment for a long time, and when ingested turns into the active form.

The dog disease sniffing experiment Method

The research was performed in Dutch teaching hospitals.

They used a two year old beagle trained to identify the smell of C difficile. The dog was tested with and tested on 300 patients (30 who had C difficile infection and 270 that did not.

" The dog was guided along the wards by its trainer, who was blinded to the participants’ infection status. Each detection round concerned 10 patients (one case and nine controls). The dog was trained to sit or lie down when C difficile was detected."

However the dog was also tested with detecting the bacteria in stool samples.

Dog infection Sniffing results

The dog's 'sensitivity and specificity' for identifying C difficile in stool samples were both 100% (95% confidence interval 91% to 100%).  That is, during the detection rounds of the 300 people, the dog correctly identified 25 of the 30 infected cases  and correctly identified as being not infected, 265 of the 270 people.

Regarding stool samples:  The dog was presented with a total of 100 stool samples: 50 were positive for C difficile and 50 were negative. The dog gave a positive response to all 50 positive samples and a negative response to 47 of the 50 negative samples.

You may wonder about the value of this as such a bacterium is surely rare?  Not quite. The bacteria is commonly found in: hospitals, nursing homes, extended care facilities, and nurseries for newborn infants.

Then you might think that is OK, as you rarely go to such places. But if you consider that the non active spores can exist  a long time in the environment, then turn active inside of you, then you may have a little more concern for the experiment.

Added to the commonality of the places that it can be found, here is a non exhaustive list of the typical places inside of these places that it has been found: bedpans, furniture, toilet seats, linens, telephones, stethoscopes, fingernails, rings (jewellery),floors, infants' rooms, diaper pails, pets.

Not only is the above information interesting, but did you know that Clostridium difficile infection is common, particularly in people in healthcare facilities who have received antimicrobials. Where of course an "Antimicrobial" is a liquid chemical that kills or inhibit the growth of microorganisms. Microorganisma such as bacteria and fungi. Did you know that one of the most common antimicrobial drugs is penicillin - which suggests that if you go to hospital, and get a penicillin shot, you may also pick up Clostridium difficile

What does C difficile bacteria do?

It causes toxin mediated intestinal disease, with symptoms ranging from mild diarrhoea to severe pseudomembranous colitis, and toxic megacolon. Infection of the bacteria can either be through the environment (touching something infected) or via people.

How common is the bacteria?

nosocomial C difficile infection in European countries occurs at the rate of 17.5-23 infections per 10,000 admissions. Specifically in the UK the mean incidence is 50/10 000 admissions. It is serious enough, and difficult enough to control that outbreaks have lead to ward closures and extensive infection control measures.


the study showed that a well trained dog can be vital in the detection of the Clostridium difficile in stool samples and clinical wards.

The only limitation seems to be training time of the dog, and where it is allowed to go. The experiment trialled the dog in children wards, but due to the high excitability of the subjects, the trial was abandoned.

The researcher's also came up with the following "Unanswered questions" that may lead to further studies:

+  what does the dog actually smell—is it a certain quantity of bacteria, toxins, or other bacterial products?

+ How does the dog respond to stool samples that are negative for toxin by enzyme immunoassay but positive by toxigenic culture, cytotoxicity assay, or nucleic acid amplification tests?

+ does the dog respond to patients early in the course of the infection, or those with asymptomatic carriage of toxigenic and non-toxigenic strains?

Even bigger questions should be where can such dogs be used (airports, prisons) or other lock down situations. AND what other diseases can they smell?


Article by Bruce Dwyer. If you wish to use any of this information please use a LINK reference to

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Using a dog’s superior olfactory sensitivity to identify Clostridium difficile in stools and patients: proof of principle study Marije K Bomers et al, 13 December 2012


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