Canine Corner

The human-animal bond

Infection Detection Dogs

Dogs can accurately sniff out patients affected by "superbug" infections.

Dog canine infection detection C. difficile Beagle Cliff

While science has made impressive breakthroughs in the field of medicine, sometimes the new health promoting procedures that are developed lead to unexpected complications. It seems that in some cases help for some of these difficulties comes from a very low-tech source — as the French poet philosopher and politician Alphonse de Lamartine, said, "When man is in trouble, God sends him a dog."

The crisis that we are focusing on here has to do with the fact that the widespread use of antibiotics has been responsible for problems associated with so-called "superbug" infections. These usually strike patients who are in the hospital for other reasons. One of the more problematic of these is Clostridium difficile (usually referred to as C. difficile). This infection most commonly occurs in older people who have recently had a course of antibiotics in the hospital. The antibiotics kill off the normal helpful bacteria in the intestines and C. difficile takes over the gut. It releases toxins which cause diarrhea, fever, nausea, abdominal pain, loss of appetite, and may even cause ulcers that eat their way through the intestinal walls. Approximately 7 percent of the people infected will die within 30 days, and the most recent statistics found that C. difficile was listed as a cause contributing to death for around 21,000 people per year in the United States alone. Antibiotic treatment can be difficult due to the bacteria's drug resistance, its structure which includes a protective membrane, and the release of extremely hardy spores. Over the past 20 years the rate of infection has been rising steadily probably due to a corresponding increase in the use of antibiotics and an aging population. Recently there have been several large hospital outbreaks of C. difficile that were so severe that they required extensive infection control measures and sometimes even ward closures.

The most important procedure used to prevent transmission and spread of the infection involves early detection of the people carrying the bacteria and then isolating them from the general hospital population. However, the diagnostic tests to identify infected patients can be expensive and they require special equipment and expertise. Much more important from the standpoint of control is the fact that these tests are slow and in some cases can delay treatment for up to a week.

The most recent breakthrough that may help to control the spread of the infection comes from the fact that some people have suggested that the diarrhea due to C. difficile has a specific smell. Obviously dogs have a superior sense of smell compared to that of humans. There have been a number of reports of dogs being able to be trained to detect various forms of cancer. Dogs' sense of smell can even detect the fluctuations of blood sugar levels in diabetics (click here to see more). Furthermore dogs' scent recognition ability can be used for much more exotic detection tasks (click here or here to see some examples). This prompted Marije Bomers and a team of researchers in the Netherlands to try to see if dogs could be trained to identify C. difficile. A Beagle named Cliff was chosen for the task. Starting with stool samples, he was taught to identify the scent caused by the change in body chemistry in infected individuals. He was then trained to sit or lie down when he detected C. difficile. After two months of schooling, the dog’s detection abilities were formally tested on 50 C. difficile positive and 50 C. difficile negative stool samples. He correctly identified all of the 50 positive samples and 47 of the 50 negative samples. In the terminology of statisticians this equates to 100% sensitivity and 94 percent specificity (sensitivity measures the proportion of infected samples correctly identified, while specificity measures the proportion of uninfected correctly identified). Next the dog was then taken on to two hospital wards to test his detection abilities in patients. This was done by simply walking him through the wards, passing by each bed without touching the patients or making contact with any of the furniture. Cliff correctly identified 25 out of 30 cases (sensitivity 83 percent) and 265 out of 270 negative controls (specificity 98 percent). Having proven that a dog can detect C. difficile, the researchers reported their findings*, and Cliff, the Beagle, was retired.

Now fate sets in. Two years after Cliff was used to prove the possibility of an infection detection dog, there was an outbreak of C. difficile at the Vrije Universiteit Hospital in Amsterdam. At this point Marije Bomer's team had a chance to see how a dog would perform under actual field conditions when the diagnostic ability of the dog could really make a difference. So the research group brought Cliff out of retirement, and without any refresher retraining, he was put to work again — this time to screen patients who were in potential jeopardy of coming down with or transmitting C. difficile while they were in the hospital being treated for other conditions. In the end the little Beagle screened 371 patients. The dog correctly identified 12 out of 14 patients with C. difficile infections (a sensitivity of 86 percent) and 346 out of 357 infection free patients (a specificity of 97 percent). It is interesting that of the few patients misidentified as being infected when they were not, 18 percent displayed the infection within three months, while only 3.5 percent of those at the dogs declared infection free did so. The full set of results have been accepted for publication in the Journal of Infection**.

This recent study confirms that a trained detection dog can accurately detect C. difficile in hospitalized patients during an outbreak. The accuracy of the dog is quite high and the time spent identifying infected patients is quite small — it takes the dog only about 10 minutes to completely inspect all of the patients in a given ward. Such rapid diagnosis of infected individuals can allow them to be isolated from the general hospital population to prevent spread of the disease and to allow immediate treatment to be started. The cost of keeping a trained detection dog the size of the Beagle is minimal, certainly when compared to the cost of providing the complex diagnostic equipment and trained personnel in every hospital in order to do the same task. And of course, the lives of patients potentially saved by the quick screening of the dog are priceless.

Stanley Coren is the author of many books including: The Wisdom of Dogs; Do Dogs Dream? Born to Bark; The Modern Dog; Why Do Dogs Have Wet Noses? The Pawprints of History; How Dogs Think; How To Speak Dog; Why We Love the Dogs We Do; What Do Dogs Know? The Intelligence of Dogs; Why Does My Dog Act That Way? Understanding Dogs for Dummies; Sleep Thieves; The Left-hander Syndrome

Copyright SC Psychological Enterprises Ltd. May not be reprinted or reposted without permission

Data from:

* Bomers MK, van Agtmael MA, Luik H, van Veen MC, Vandenbroucke-Grauls CM, Smulders YM. Using a dog's superior olfactory sensitivity to identify Clostridium difficile in stools and patients: proof of principle study. British Medical Journal (2012) 345:e7396.

** Bomers MK, van Agtmael MA, Luik H, Vandenbroucke-Grauls CM, Smulders YM. A detection dog to identify patients with clostridium difficile infection during a hospital outbreak.Journal of Infection (2014), doi:1016/j.jinf.2014.05.017.

Stanley Coren, Ph.D., F.R.S.C., is a professor of psychology at the University of British Columbia.

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