Before the development of modern diagnostic equipment, doctors had to rely on their senses to make a diagnosis; diabetes is marked by fruity breath; the breath of patients with cystic fibrosis smells acidic and typhoid smells like baked bread (Stitt 1995). The stool of C.difficile infected patients smells like horse manure; there is even something called the ‘breath of the dead’, fetor hepaticus. And that doggy smell? It is usually associated with seborrhea.
My first blog post on detector animals was about tuberculosis detecting bees, then about dogs detecting mange in wildlife. This paper from BMJ reports yet another use for a dog’s wonderful nose; the detection of Clostridium difficile. [Follow the BMJ link to a 10 minute video]
Noting the distinctive odour of diarrhea in C.difficile-positive patients the researchers advanced the idea that a dog might be able to detect an odor specific to C.difficile. For this purpose, a 2-year old beagle named Cliff was clicker-trained to give a passive indication (lie down) to toxigenic C. difficile.
” The dog used in this study was a 2 year old male beagle. A professional detection dog instructor (HL) trained the dog to identify C difficile in stool samples and, if this proved possible, in patients. A reward based training method was used in which the correct behaviour was reinforced, for instance by providing a treat. The dog was taught to sit or lie down if a specific scent was detected. He had not received previous training in detection.”
The results were that with stool samples the dog gave a perfect score of 50/50 with positive samples and 47 negative responses out of 50 negative samples, 3 of the responses were ‘inconclusive.’ If we consider the inconclusive indications as negative indications then the dog scores 100% (95% CI 91% to 100%) for sensitivity and specificity. If we consider the inconclusive responses are positive indications then Cliff scores 100% for sensitivity and 94% (CI 83% to 98%) in specificity.
It is doubtful that dogs will start roaming hospitals or hanging out in the labs checking out samples for C. difficile. The success reported in this study indicates that quick detection is possible using a different modality than the one currently in use. These findings also suggest that it might be possible to manufacture “electronic noses” or even hand-held biosensors that will do the same job, making it possible for any health facility to rapidly detect and hopefully stop the spread of C.difficile.
A dog’s sense of smell continues to amaze, who knows what job they will do next.
Stitt WZ, Goldsmith A. (1995) Scratch and sniff. The dynamic duo. Arch Dermatol. 1995 Sep;131(9):997-9.
Bomers, M., van Agtmael, M., Luik, H., van Veen, M., Vandenbroucke-Grauls, C., & Smulders, Y. (2012). Using a dog’s superior olfactory sensitivity to identify Clostridium difficile in stools and patients: proof of principle study BMJ, 345 (dec13 8) DOI: 10.1136/bmj.e7396
van Nood E, Vrieze A, Nieuwdorp M, Fuentes S, Zoetendal EG, de Vos WM, Visser CE, Kuijper EJ, Bartelsman JF, Tijssen JG. (2013) Duodenal infusion of donor feces for recurrent Clostridium difficile. The New England journal of medicine, 368(5), 407-15. PMID: 23323867