Where does Clostridium difficile really come from?

It seems like half the people I know have sent me this article about Clostridium difficile for comment. It’s a news article about a New England Journal of Medicine research paper (Eyre et al 2013).

The paper has some interesting findings. They used whole-genome sequencing to look at the genetic makeup of C. difficile from infected patients in a hospital. It was an impressively comprehensive study that looked at samples from over 1000 patients. By looking at the DNA of C. difficile isolates from patients, they could see when the bacterium was likely passed between patients and when it was not. Over the 3 year study period, almost half of the C. difficile isolates were different enough genetically from other isolates to indicate they didn’t come from someone else in the hospital.

I don’t think it can be said with 100% confidence that all those C. difficile strains were truly acquired outside of the hospital (i.e. in the community), since they only looked at people with C. difficile infection. People can also carry the bacterium without any signs of disease, and it’s possible that such individuals were a source of infection for others in hospital. Since the researchers weren’t testing for subclinical carriers, they don’t know whether "unrelated" cases were from strains acquired outside the hospital or from undetected carriers in the hospital. I suspect a lot of cases truly do originate outside of the hospital, though, and this goes against current dogma that most hospital cases are acquired by spread between patients.

I think we're eating it all the time, probably from animals, and most of us get it and it doesn't matter."

  • I’ve been saying that for years. I think we probably ingest C. difficile every day from food, water and various environmental sources. Most often, it doesn’t cause of problem. Figuring out why it does in some situations needs to be a priority.

If you don’t look, you don’t find. It’s been a self-fulfilling prophecy for years with C. difficile:

  • People (supposedly) only get C. difficile if they’ve been in hospital on antibiotics.
  • If you don’t have those risk factors, you don’t get tested for C. difficile.
  • So... we never diagnose C. difficle in people who haven’t been in hospital or on antibiotics.

It’s been shown for many years (but often overlooked) that C. difficile may be a common cause of diarrhea in people in the general population and those without traditional risk factors.

more and more deep cleaning ain’t going to do any good.

  • (Not the typically grammatical approach for a University of Oxford researcher, but...) The point is that you can do everything to control C. difficile in the hospital and you still won’t be able to control all cases. I agree with that. However, care must be taken to ensure this doesn’t get translated into “most C. difficile is coming from outside the hospital anyway, so why should we spend so much time and money on cleaning and infection control?”

These findings have led some people to point the finger at animals as important sources of C. difficile.

  • I think this is taking the animal link too far. This is coming from someone who was one of the first and is still one of the few people to have looked at C. difficile in food. So if anything, I stand to benefit from any links between food and C. difficile (since more concern and more interest = more research opportunities).

Clostridium difficile expert Nigel Minton, from the University of Nottingham, had a nice balanced comment: "Obviously hospital infection control measures have had a big impact on C. difficile cases. But there is a growing feeling that community-acquired C. diff is equally important and there are also studies suggesting possible transmission to humans from animals. This has quite clearly been demonstrated from pigs to humans in the Netherlands."

  • I think this means that we need to pay attention to the potential role of animals, but not just dump the blame on them with no further study. The key point is we need proper research to figure out how C. difficile circulates in the community and what role animals, food, water and the environment play in transmission.

and “Nursing homes are a major factor as well, it is where you get a lot of people susceptible to infection."

  • That’s another interesting area and one that we’re currently investigation.

Do you know what's in your dog's 'bully stick'?

I mean that two ways.

1) Do you know what a bully stick actually is?

2) Do you know what's in it?

A recent study headed up by Dr. Lisa Freeman, published in this month's Canadian Veterinary Journal (Freeman et al., CVJ 2013;54:50-54), looked into this by asking people what they thought bully sticks were made of, and testing the treats for calorie count and bacterial contamination.

The answer to question 1 is: bully sticks are raw, dried bull penis (which explains the need for a cuter name).

  • Only 44% of people surveyed knew that.

Also, bull penis is considered a by-product, yet 71% of people that fed bully sticks to their dogs said they avoid by-products in food.

  • This just shows a lack of understanding about what by-products are and their nutritional value. Many people classified things that are prohibited from by-products as being by-products, such as hooves, horns, road kill and euthanized pets. By-products aren't always bad and can, in fact, have good nutritional value. Also, they can be environmentally friendly and ethical since they are often made from nutritionally valuable parts of the animal that might otherwise be thrown out, thereby providing food for pets without taking anything out of the human food supply chain.

"What's in it?" was approached from 2 standpoints:

Firstly, caloric content was assessed.

  • Treats often get ignored when thinking about a pet's caloric intake, but calorie-dense treats can certainly contribute to obesity. Fifty percent of people surveyed underestimated the calorie counts of bully sticks. The average caloric density was 3 calories/gram, and given the variation in size of bully sticks, total calorie counts for a single stick ranged from 45-133 calories (9-22 calories/inch). So, yes, size matters.

Secondly (my bit part in this study), we looked at contamination by a select group of bacteria.

  • Salmonella wasn't found, which was encouraging since high Salmonella contamination rates have previously been found in some treats (mainly pig ears), and contact with pet treats has been implicated in some outbreaks of salmonellosis in people. We found Clostridium difficile in 1 treat (4% overall). That doesn't worry me too much since it's increasingly clear that we encounter this bacterium regularly. With common sense and handwashing, it's probably of little risk, but in some people (e.g. elderly, people on antibiotics, people with compromised immune systems) it might be more of a concern. We also found methicillin-resistant Staphylococcus aureus (MRSA) in one sample. This was a "livestock-associated" MRSA strain that can cause infections in people, but the risk is unclear. Theoretically, it's a potential source of exposure. If someone got MRSA on their hands from the treat then touched their nose (where MRSA likes to live) or a skin lesion (where it can cause an infection), then it could potentially cause a problem. Overall, the risk is probably quite low, but it's another reason to wash your hands after handling treats.

None of this means dog owners need to avoid bully sticks. It does mean that you should pay attention to what you feed your pet, think about treats when considering your pet's caloric intake (especially if your dog is overweight), keep treats away from high risk people (e.g. don't use a bully stick as a teething toy) and wash your hands after handling dog treats (of any kind).

Photo: A variety of bully sticks (also known as pizzle treats) often fed to dogs as chew treats (photo credit: Gergely Vaas 2006 (click for source))

C diff sniffing dog

About 500 people have sent me this article over the past week, so I guess I should get around to making some comments. The article entitled "Using a dog’s superior olfactory sensitivity to identify Clostridium difficile in stools and patients: proof of principle study" (Bomers et al 2012) is in the Christmas edition of BMJ, an edition in which they typically publish something fun or light. The study describes the use of a dog trained to sniff out C. difficile, an important cause of diarrhea people, especially hospital patients. The premise is that dogs could be used as a rapid and cheap way to diagnose C. difficile infection, and therefore allow for earlier treatment and implementation of enhanced infection control measures.

There were 3 components of the study:

1) Detection of C. difficile on a culture plate

The dog was trained using culture plates containing C. difficile. That's how they have to start, but detecting C. diff on a culture plates is pretty easy. I can do that, and my nose is nowhere near as good as a dog's. Clostridium difficile has a very characteristic odour on a culture plate and odour is one of the methods that's commonly used to determine whether C. difficile might be present on the plate. 

2) Detection of C. difficile in stool

For this, the researchers set the bar pretty low. A positive fecal sample was considered one that was culture-positive positive on a test to detect the C. diff toxins. We know toxin tests are pretty insensitive (they give a lot of false-negatives), which is why there's a major movement to replace them with molecular tests. By requiring the sample be positive on both culture and toxin test, it means that the samples had to have been quite positive to be considered (i.e. they didn't test the dog with "weaker" positive samples that may have had less C. diff and C. diff toxin in them). That weakens the results a bit, but they're still interesting.

They presented the dog with 50 positive and 50 negative samples. The dog gave a positive response to all 50 positive and a negative response to 47/50 negative samples.

3) Detection of C. difficile in patients

Here's where it gets more interesting and potentially more relevant, since the real value in a sniffer dog would be to detect C. diff directly from patients, as a rapid and cheap screening tool.

For this part, they enrolled 30 patients with C. difficile infection and 270 controls. One problem I have is that 94% of their controls were non-diarrheic. It raises questions about whether the dog is detecting C. difficile or just diarrhea, since the groups don't just differ by their C. diff status, as would be most appropriate for a control group. The more differences there are between the groups, the greater the potential that a difference other than the one of interest (i.e. C. diff status) is actually the thing that's being detected. There' a big difference between a dog that can detect C. difficile and a dog that just detects diarrhea.

Another issue is that some C. difficile strains don't produce toxins and are not able to cause disease, but they'd presumably be detected the in the same way based on odour, in contrast to tests that are based on detection of the bacterial toxin or genes that encode toxin production.

Anyway, the dog correctly identified 25/30 (83%) cases and 265 (98%) controls. Not as good as current molecular tests but pretty remarkable, nonetheless.

Overall, it's an interesting story and shows how good a dog's nose can be, how smart (some) dogs are, and how thinking outside the box can result in some interesting ideas. Though I don't think diagnostic testing companies have much to worry about at this time in terms of competition from sniffer dogs.

Cool concept. Fun paper. Not coming to a hospital near you in the near future, but not something to completely dismiss.

(click image for source)

Clostridium difficile and hospital visitation dogs

A couple questions that I received about C. difficile and hospital visitation dogs:

Is there any concern about cross contamination from dogs/handlers that visit health facilities and get contaminated by C. difficile? I see on this site a concern about dogs being contaminated by visitation and I wonder if the Delta Society has considered this to be an acceptable risk.

Dogs (and handlers) could be sources of C. difficile in hospitals. We have shown clearly that dogs that visit hospitals are at increased risk of shedding C. difficile in their feces, presumably because they ingest C. difficile spores from the hospital environment and/or patients' hands. All dogs that go into hospitals are at risk, with dogs that lick patients and that are allowed up on beds at increased risk (Lefebvre et al 2009). We have also shown that the dog's body can become contaminated with C. difficile after visiting a hospital.

Should there be a period of time mandated between visits to account for possible contamination?

That's hard to say, but probably not. Contamination is a potential problem and certainly occurs, but we don't know how long it lasts nor whether providing a "rest" period actually does anything. Clostridium difficile spores, the form of the bacterium that would be present on a dog's coat, are very environmentally tolerant and can survive for years. Therefore, giving a few days break in between visitation would not result in the bacteria dying. However, some spores would presumably be physically removed over time, through shedding of hair, grooming and other activities. Based on that, it's plausible that the longer the time between visits, the less likelihood of contamination still being present. Whether this actually helps, we don't know.

What to do?

Among other things, we need to consider whether there is actually any evidence of risk. We don't know whether dogs are able to transmit C. difficile in hospitals. My assumption is that there is some degree of risk, but it's limited and can be controlled with good hygiene and the use of basic visitation practices, as highlighted in the "Guidelines for animal-assisted interventions in healthcare facilities" (American Journal of Infection Control, 2008).

Another thing to consider is whether there are any measures that can be taken to reduce potential risks, while maintaining a practical and effective visitation program. A key component of this is knowing that there are factors that make it more likely that a dog will be exposed to C. difficile during visitation. If a specific subset of dogs is at increased risk, then you have a clearer way to approach it. In this case, dogs that are allowed to lick patients and that are allowed on beds are at increased risk. These activities are modifiable - you can prohibit them without having a significant impact on the visits. Licking can be prohibited. Dogs can be kept off beds unless it is required, and when that's the case, they can be placed on a towel or some other barrier to reduce their exposure to C. difficile from the bed. Additionally, we know that if a dog is being treated with antibiotics, it's more likely to shed C. difficile, so dogs that are being (or have recently been) treated with antibiotics should be excluded from visitation.

For C. difficile to be a problem, it has to go from human or animal feces to a patient's hands and then to a patient's mouth. There are multiple potential interventions to interrupt this chain of transmission. At the end of the day, however, hand hygiene is the key. If people wash their hands before and after touching the dog, there should be much lower risk of disease transmission. A problem is that when I say "hand washing," I mean hand washing - not use of an alcohol-based hand sanitizer. Clostridium difficile spores are resistant to alcohol. That creates a conundrum because the use of alcohol hand sanitizers, a common and recommended hand hygiene method, doesn't have the ability to kill C. difficile. Since not all visitation patients are able to get up and go to a sink, that complicates C. difficile control.

(click image for source)

I have Clostridium difficile...Should my dog be tested?

I get this question surprisingly often. In one way, that's good because it shows increasing awareness of the potential for interspecies transmission of microorganisms. In some situations, when a person has an infection, the pet should be considered in case it was the source of the infection and/or in case it's at risk of becoming infected by the person.

Clostridium difficile is a very important cause of diarrhea (and sometimes more severe intestinal disease) in people. Previously it usually only affected people confined to hospitals and people being treated with antibiotics, but it's now being identified more often in people in the community.

The potential for interspecies transmission of this bacterium is real.

  • C. difficile can be found in a small percentage of healthy dogs and cats.
  • The strains of C. difficile in dogs and cats are almost always the same as those found in people. My lab has one of the largest collections of C. difficile around and we only have a couple of C. difficile isolates from dogs and cats that we have not found in people.
  • Dogs that visit human hospitals are at increased risk of shedding this bacterium in their stool, and certain types of contact with people have been identified as increasing this risk (Lefebvre et al 2009).
  • Dogs owned by an immunocompromised person are at increased risk of shedding C. difficile (Weese et al 2010), presumably because the person is more likely to shed the bacterium and subsequently infect the pet.
  • Dogs that are owned by people being treated with antibiotics are more likely to shed the bacterium (Lefebvre et al 2009). That's probably because, as with immunocompromised people, when someone's being treated with antibiotics, they have a greater likelihood of shedding C. difficile and their dog subsequently becomes infected.

However, there's currently no indication that testing is needed.

  • What would the results tell you? If you identify C. difficile in your dog and you have a C. difficile infection, does that mean that you were infected by the dog, you infected the dog or you were both infected by the same source?
  • What would you do with the results? There's no indication to treat the dog if it's positive and healthy.
  • What testing would you actually get done? Testing for diagnosis of C. difficile disease usually involves trying to detect bacterial toxins in stool. The tests aren't meant to be used on normal stool. To really know what's going on, you'd need to have the bacterium cultured from your pet's stool as well. Not many labs can do that. Furthermore, to get really useful information, you'd also need to get your stool cultured and, if C. difficile was present in both you and your dog, molecular typing would be required to show that they were the same strain. Very few places can do that. Even with that information, at the end of the day, finding the same strain in you and your pet doesn't tell you more than the fact that the bug probably moved between you and your pet, in one direction or another.

If you have C. difficile, it's reasonable to take precautions to reduce the risk of infecting other individuals, both human and animal:

  • Practice good hygiene. Wash your hands thoroughly after using the washroom.
  • Don't let your dog drink out of the toilet.
  • Use antibiotics judiciously. If your pet is being treated with antibiotics and you have C. difficile, there's probably a greater chance of your pet picking up the bacterium.
  • If you have C. difficile and your pet develops diarrhea, tell your veterinarian. It's important that they know that your pet may be at higher risk of C. difficile infection.

If you have recurrent C. difficile infections, considering the pet as a possible source might be reasonable, but we don't currently know what role pets may play. As described above, investigating your pet as a possible source would require culturing stool from both you and your pet, having both typed using molecular tests, and a joint effort involving your veterinarian and physician.

Antibiotics, pets and Clostridium difficile

Clostridium difficile is a high-profile bacterium, being an important cause of illness and death in people. It can also be found in various animal species, including dogs and cats. In a study we published earlier this year (Lefebvre et al, Journal of the American Veterinary Medical Association, 2009), factors associated with acquisition of Clostridium difficile by dogs involved in hospital and non-hospital therapy programs were assessed. Things that were significantly associated with a dog acquiring C. difficile were:

- Contact with human hospitals: Not too surprising since it's clear that hospitals can be highly contaminated with C. difficile and the hands of some patients petting the dogs are probably also contaminated.

- Contact with children: Most parents know that kids are biohazardous (we've getting over a round of illness in our house brought home by the kids - not an unusual event). Whether the increased risk for dogs is because kids have higher rates of C. difficile carriage, or because they have closer contact with dogs (with little hygiene) or some other factor isn't clear.

- Recent use of antibiotics: No surprise here. Antibiotic use is a well-recognized risk factor for C. difficile, since antibiotics can disrupt the normal protective bacterial population of the intestinal tract and allow C. difficile to grow.

- Recent use of antibiotics by a person in the house: I think this is a fascinating result and a great example of the close inter-relatedness of people and pets microbiologically. What presumably happens is that when someone is treated with antibiotics, they are more likely to acquire C. difficile and pass it in their feces. By doing so, there is a greater chance that their dog will be exposed to C. difficile, perhaps from the person's hands or the household environment. (The toilet would be a great source if the dog's a toilet-drinker). The implications of this, for both dogs and people, are unclear. It could be primarily an academic risk (i.e. of little practical significance), or it could be that interspecies transmission of C. difficile plays a role in disease in both species. We simply don't know at this point.

This is also a good example of why educational efforts regarding prudent antibiotic use need to be directed at both animal and human healthcare.

More information about Clostridium difficile can be found on the Worms & Germs Resources page.

Image source: www.sciencedaily.com/releases/2009/05/090507101820.htm

Preventing infections in the home

There is a nice, concise commentary in the most recent issue of the Canadian Medical Association Journal about preventing infections in the home. It covers three important organisms: MRSA, Clostridium difficile and vancomycin-resistant enterococci (VRE). An excellent aspect of this particular commentary is its relatively low-key approach, with an emphasis on routine, basic practices such as hand hygiene. It also includes some comments about pets that are similarly well-balanced and go along with a lot of what we've been saying on Worms & Germs Blog. For example, in discussing MRSA, they state:

"Because domestic pets may serve as a reservoir of MRSA, hands should always be washed thoroughly with soap and water after contact with animals or their feces. In cases of outbreaks within a family of an infection caused by community-associated MRSA that cannot be arrested, a colonized pet may need to be temporarily removed from the home. However, it may be prudent to re-emphasize the importance of personal hygiene before taking such a drastic measure."

Overall, it's a commentary you might find useful. It can be downloaded by clicking here.

Clostridium difficile in the household environment

Another study we presented at the recent European Conference of Clinical Microbiology and Infectious Diseases was about Clostridium difficile in the household environment. In the study, we collected samples from various locations and surfaces in households, as well as five fecal samples (one per day) from pets, and tested them for C. difficile. Some of the most interesting findings included:

  • Clostridium difficile was found in one or more locations in 31% of households. The toilet was, not surprisingly, the most common site, but the kitchen sink, refrigerator and dog food bowl were close behind.
  • The most common strain found in households was the international outbreak strain ribotype 027. Ribotype 078, a strain that is commonly found in food and food animals, was the second most common type.
  • Clostridium difficile was isolated from 10% of dogs and 10% of cats, however in most cases only 1 of the 5 daily samples was positive.
  • All of the strains of C. difficile found in pets were strains that have previously been recovered from people. This fits with previous reports that strains found in animals tend to be the same as those found in people, and supports concerns that C. difficile can be transmitted between humans and animals.
  • In no households were C. difficile strains found in the pets the same as those found in the environment.  This suggests that pets are not an important source of household C. difficile contamination.
  • Dogs that lived with an immunocompromised person were 7.9 times as likely to shed C. difficile than other dogs. Presumably, immunocompromised people are more likely to carry C. difficile and subsequently transmit it to their pets.

More information about Clostridium difficile can be found on the Worms & Germs Resources page.

Dirty hands, Dirty therapy dogs?

A study published recently in the Journal of Hospital Infection (Lefebvre & Weese, 2009) looked at contamination of the haircoat of animals used in hospital visitation programs. In the study, Dr. Lefebvre petted animals that were going into a hospital and we cultured her hands.  Then when the dogs finished their visits she petting them again and we re-cultured her hands.  We tested for MRSA and Clostridium difficile, two important causes of hospital-associated infections. The goal was to see if the dogs' coats could become contaminated, presumably by patients' hands, during regular visits. The dogs' paws were also tested before and after to see what they picked up walking around the hospital.

After being in the hospital, one dog (4%) was found to have C. difficile on its feet. The strain that was recovered (ribottype 027/NAP1) is a strain of great concern, being it has caused outbreaks of illness internationally. The fact that there was C. difficile on the dog's paws, which was presumably picked up from the floor in the hospital, isn't exactly surprising. It shows that contact with dogs' feet (e.g. shaking a paw) could be a source of exposure to people in hospitals, and at home, and that dogs could be exposed to C. difficile after hospital visits by licking their paws. We previously demonstrated in another study that visitation dogs are at high risk for picking up C. difficile during visits.

The more important aspect of the study was what ended up on Dr. Lefebvre's hands after petting the dogs - a very common type of contact with dogs in hospitals and at home. She picked up MRSA from the coat of one dog (4% of dogs overall) after it had been in the hospital. The dog was not an MRSA carrier, and it did not have contact with anyone known to be carrying MRSA during its visit. Presumably, there was someone in the hospital that was an unknown carrier. If MRSA was on the person's hands, they could have transfered the MRSA to the dog's coat. The important part is that this MRSA was then able to spread to someone else's hands (Dr. Lefebvre's, in this case). This is a potential route of transmission of MRSA to patients during hospital visitations, and to other people these dogs might encounter outside of hospitals. The same thing could presumably happen with other infectious agents, including bugs like norovirus and influenza. These can't infect dogs, but dogs could potentially be short-term vectors of these viruses and spread them around a hospital.

The good thing about all this is that some basic guidelines can greatly reduce the risk of transmission:

  • Patients should wash their hands  or use an alcohol-based hand sanitizer before  (to reduce the risk of depositing something on the pet's coat) and after (to reduce the risk of picking something up from the pet's coat) touching a pet.
  • Pets should be kept off beds unless a disposal/washable barrier (e.g. drape, towel) is kept between the pet and the bed sheets, to prevent dirty feet from infecting the patient's living space/clothes/sheets.
  • People should not "shake-a-paw" with pets in hospitals.

All these precautions can be taken without compromising the benefits of hospital pet visitations. More details about guidelines for hospital visitation aniamls can be found in an earlier post. More information about Clostridium difficile and MRSA can be found on the Worms & Germs Resources page.

Your mother was right! Wash your hands

You may notice a recurring theme in many of our posts and on virtually all of the information sheets on the Worms & Germs Resources page: an emphasis on handwashing. There is increasing emphasis on hand hygiene (i.e. hand washing and use of alcohol hand sanitizers) education in hospitals because the hands of healthcare workers are a major (if not the most important) means of disease transmission between patients. Despite hand hygiene being easy, cheap and effective, people rarely wash their hands as often as they should, and they often don't do it properly.

Most of the research about hand hygiene that has been published has focused on its use and impact in human hospitals, but this area is now also being studied more with regard to animals and veterinary medicine. A study published earlier this year in Veterinary Microbiology provided more evidence that hand hygiene is a critical infection control measure when dealing with animals. The study, coordinated by Dr. Maureen Anderson (of Worms&Germs fame) looked at MRSA carriage rate in veterinarians who work with horses. In addition to finding a high rate of MRSA carriage among these veterinarians (which was consistent with other reports indicating that equine vets are at higher than average risk for exposure to MRSA), the study looked at factors associated with MRSA carriage. Vets that reported routinely washing their hands between farms and those that reported washing their hands after contact with potentially infectious cases had a significantly lower rate of MRSA carriage. That should come as absolutely no surprise, but it's one more piece of evidence that we need to pay more attention to this routine infection control measure, in human hospitals, in veterinary environments and in households.

Remember, the 10 most important sources of infection are the fingers on your hands!

Click here for instructions on how to wash your hands properly.


If you are looking for an interesting website to play around with, you should try HealthMap. This is a website created by the Harvard-MIT Division of Health Sciences and Technology that maps infectious disease reports from various sources. You can search by region and see what disease problems have been reported recently, or select specific diseases and find out where they've been reported.   Some examples are shown below. The top image shows all disease reports worldwide (in the last 30 days), while the bottom image shows reports of Salmonella in North America during the same time period. The site relies on reports of diseases (many cases of various diseases occur but are never reported), so it focuses mainly on outbreaks or high profile cases , but it is still quite interesting.

Above: All reported disease outbreaks/cases worldwide in the last 30 days.
Below: Reported outbreaks/cases of Salmonella in North America in the last 30 days.
See the HealthMap site for more details.

"Clostridium" in dogs and cats: what's in a name?

People often ask me questions about "Clostridium" in dogs and cats, with the impression that "Clostridium" is a specific disease. Actually, Clostridium is a large bacterial genus (a group of related bacteria), which includes species that range from harmless to deadly. Some of the more important species are described below:

Clostridium perfringens: This is a common bacterium that can be found in the stool of a large percentage of healthy animals and people. It is a common cause of "food poisoning" in people, and is probably an important cause of diarrhea in dogs and cats. Our understanding of the role of this bacterium in disease in dogs and cats is limited by the fact that it is found in so many healthy animals, so simply growing it from the stool of a diarrheic dog or cat does not prove that it is causing the animal's illness.

Clostridium difficile: This bacterium is a very important cause of diarrhea (and more severe intestinal disease) in people, and is possibly an important cause of diarrhea in dogs and cats. It is rarely found  in healthy adult pets, but is relatively common in puppies and kittens.

Clostridium botulinum: This bacterium produces the toxin that causes botulism, a potentially devastating disease that is very rare in dogs and cats. Botulism usually occurs following ingestion of food that has been improperly stored, in which C. botulinum has grown and produced its potent toxins.

Clostridium tetani: This bacterium produces the toxin that causes tetanus, which can occur in dogs and cats, however these species are relatively resistant to this disease. Tetanus usually occurs when a wound becomes contaminated with C. tetani from the soil, followed by growth of the bacterium and production of potent toxins.

Other clostridia: A large number of different species exist, and it is likely that many more clostridia are around but have not been identified and named. Many clostridia are part of the normal bacterial population in the intestinal tract. Some of these can probably also cause disease.

As you can see, "Clostridium" is more than a single bacterium or disease. An understanding of this concept, and the different disease-causing clostridia, is important.  More information on Clostridium difficile can be found on the Worms & Germs Resources page.

Image: Photomicrograph of C. botulinum stained with Gentian violet.  From CDC's Public Health Image Library (PHIL), ID number #1979.

Can dogs and cats get Clostridium difficile?

I've had this question a few times recently. There isn't really a straightforward answer, and it depends what people mean when they say 'get'. I've broken the question into a few components.

Can C. difficile be found in dogs and cats?
Yes. A small percentage (1-5%) of healthy dogs and cats carry C. difficile in their intestinal tract, and pass it in their stool. Higher carriage rates are found in certain groups, such as young animals, animals in veterinary hospitals and animals that visit human hospitals as part of therapy programs. Most animals that are carrying C. difficile do not get sick.

Does C. difficile cause disease in dogs and cats? (i.e. do they get sick?)

The answer to this one is 'probably'. I don't think we can say for sure, but C. difficile appears to be a cause of disease in dogs and cats, ranging from mild diarrhea to fatal severe colitis. There is evidence indicating that C. difficile might be one of the more common causes of diarrhea in dogs. In people, C. difficile infection is most common in hospitalized individuals and those being treated with antibiotics. The situation is different in dogs and cats, where disease seems to be most common in households (not veterinary hospitals), and in animals not being treated with antibiotics.

Information sheets on Clostridium difficile can be found on our Resources page.

Should I have my pet tested for Clostridium difficile?

I often get asked about testing of healthy pets for Clostridium difficile. This bacterium is an important cause of disease in people. While most common in people in hospitals, cases of C. difficile infection are occurring more in people in the general population. Also, C. difficile can be found  in various animals, including dogs and cats. This has led to concerns about the role of pets in C. difficile infection in people. The role of animals in human infections has not been determined, but it is plausible that C. difficile could be transmitted between people and pets, in both directions.

I have been diagnosed with C. difficile. Should my pet be tested?
No. There is no evidence that it is useful. Even if C. difficile is isolated from your pet, it would not tell you if the pet was the source. Your pet could be carrying a completely different strain of C. difficile. Molecular typing of the recovered bacteria (from both you and your pet) would be needed to determine if they are the same strain, and this type of testing is not readily available. Even if you both had the same strain, your pet could have picked it up from you. So, testing of your pet really wouldn't tell you anything.

I'm worried that I may have acquired C. difficile from my pet. Can I just have my pet treated at the same time I'm being treated?
No. Treatment of healthy pets to eliminate C. difficile is not recommended. There is no evidence that we can eliminate C. difficile from a healthy pet with antibiotics.

More information on Clostridium difficile can be found in our Resources page.

Clostridium difficile in dogs

Clostridium difficile is a bacterium that is an important cause of disease in people and has been getting a lot of press lately in this area. Associated with that has been a lot of questions about C. difficile in dogs. Here are some facts to ponder:

  • C. difficile is thought to be a cause of diarrhea in dogs in the general population, although its true role in disease is still unclear. C. difficile infection in dogs may cause mild to moderate diarrhea that is treatable.
  • Some (<5%) healthy dogs can carry C. difficile in their intestinal tract. They may never have a problem with it.
  • Dogs that visit human hospitals have much higher rates of C. difficile carriage, but we currently don't have any evidence that they are at higher risk for disease. They probably ingest the bacterium from the hospital environment and patients' hands.
  • We are highly suspicious that C. difficile can be transmitted between people and pets (in both directions), but pets are probably not a major source of infection for people.

Certain risk factors for C. difficile carriage or infection are known, including antibiotic use (people and pets), advancing age (people) and admission to a hospital (people and pets). Some of these are not avoidable. General considerations for C. difficile prevention include:

  • Don't use antibiotics unless they are actually required. This goes for people and pets.
  • Wash your hands regularly.
  • Avoid contact with dog stool, especially diarrhea.
  • Enjoy your pet. There is always a risk of disease transmission but the risk of getting C. difficile from your pet is not something to stay up worrying about.

Information Sheets for Pet Owners

INFORMATION SHEETS specifically for KIDS, for VETERINARIANS, for PHYSICIANS and for PUBLIC HEALTH PERSONNEL are also available on the Worms & Germs RESOURCES page!

Click on the highlighted topics below for information sheets. Topics that are not highlighted are in development and coming soon. Sheets for other animal species and diseases are also under development and will be added when they are available.

Diseases Other
Dogs Rabies Litter Boxes
Cats Giardia Sandboxes
Turtles Toxoplasma Cat Bites
Hamsters Leptospira Raw Meat
Rabbits Clostridium difficile Petting Zoos
Pet Birds Cryptosporidium Needlestick Injuries
African Dwarf Frogs MRSA  
Reptiles MRSP  
  MRSP (Deutsch)  
  MRSP (Francais)  
  Rat Bite Fever  
  Cat Scratch Disease  
  Lyme Disease & Ticks  


Please Remember:

  • Your veterinarian and physician are your ultimate resource for information about the health of your pets or your family.
  • Information provided here is accurate to the best of our knowledge, but infectious diseases can be unpredictable and these sheets are for general information purposes only.
  • There can be great variation in disease risks in different geographic areas. The information provided was developed for Ontario, Canada, but most of the information is relevant for other regions as well.

Research Posters

2012 International Clostridium difficile Symposium

2012 International Conference on Equine Infectious Diseases IX

2011 ASM-ESCMID Conference on Methicillin-resistant staphylococci in animals

2011 University of Guelph Centre for Public Health and Zoonoses Symposium

2011 Canadian Animal Health Laboratorians Conference

2011 Canadian Association of Clinical Microbiology and Infectious Diseases

Coming soon

  • 2011 American College of Veterinary Internal Medicine Forum, June
  • 2011 ASM-ESCMID conference on methicillin-resistant staphylococci in animals, Sept