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Man's Best Friend Sniffs Out C. difficile

A trained dog identified toxigenic strains of Clostridium difficile with 100% accuracy in stool and 83% sensitivity and 98% specificity when near patients.

Infection with toxigenic strains of Clostridium difficile (CD) causes significant morbidity and mortality and is a large and growing problem in hospitalized patients. The available tests to reveal the presence of these strains require several days to complete, increasing the likelihood of nosocomial spread.

Noting the characteristic "horse manure–like" odor of diarrheic stool from patients infected with toxigenic CD, researchers in the Netherlands postulated that dogs — whose sense of smell is far superior to that of humans — might be able to detect this odor with great sensitivity and specificity. (One of the researchers is owner and chair of Scent Detection Academy and Research, Animal Behaviour and Cognition, HL&HONDEN, Edam, Netherlands.)

A 2-year-old male beagle was trained to identify the odor of toxin-producing CD and to sit or lie down on detection of this scent. In preliminary testing involving 50 CD-positive and 50 CD-negative stools, the dog's sensitivity and specificity were 100%. Using a case-control method, the dog was then put in proximity to one CD-positive and nine CD-negative patients on detection rounds in two hospitals. This process was repeated 29 times so the dog was exposed to a total of 30 CD-positive and 270 CD-negative inpatients. The dog correctly identified 25 of the 30 case-patients (sensitivity, 83%; 95% confidence interval, 65%–94%) and 265 of the 270 controls (specificity 98%; 95% CI, 95%–99%).

Comment: The authors note several limitations of this proof-of-principle study, including the variability of both trainers and dogs and, more importantly, the fact that many of the CD-positive patients had been moved to a single room (which could have influenced the trainer — and thus the dog's response). Further experience in this method is warranted and may prove very rewarding.

— Stephen G. Baum, MD

Published in Journal Watch Infectious Diseases December 19, 2012

Citation(s):

Bomers MK et al. Using a dog's superior olfactory sensitivity to identify Clostridium difficile in stools and patients: Proof of principle study. BMJ 2012 Dec 13; 345:e7396. (http://dx.doi.org/10.1136/bmj.e7396)

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