Animal-assisted therapy is a huge topic: almost 1500 hits using those terms alone. There is no way I am going to cover all of them and do them justice. Instead I am going to cherry pick, er, I mean, select references of interest to illustrate issues surrounding animals in the hospital. Sometimes I get the impression that readers of the blog expect encyclopedic knowledge and understanding of a topic whenever we put pixel to screen. That is only true of the other contributors to the blog, not me.

I would like to mention that I do, in fact, like animals, even dogs. I loathe most dog owners, as confirmation bias suggests there is no such thing as a considerate dog owner. But I never have contact with the dogs that don’t bark, that don’t crap on my yard, that don’t run up to me to nip at my legs. I only see the dogs that their owners allow to behave in ways I would never allow a human to behave.

It is no surprise that my kids have grown up mostly animal free. My eldest did wear me down and I bought him a hamster. It promptly bit me, drawing blood. Great, I thought, LCM. Just what I need. Then in the dead of winter it escaped, fell down a heating duct (we were putting in new floor) and electrocuted itself on the heating coils so every time the heat turned on we smelled rotting, roasting hamster. It cost $500 to take the furnace apart and clean it. Good thing it wasn’t a beagle. That was enough pets in the house for me.

Animals have multiple uses in the medicine, from testing new drugs (how I learned rabbits can scream) to various and sundry, well just various, forms of therapy. As was alluded to recently in the comments, take a noun, add the word therapy, and voila, you have a treatment for patients.

Not that animals are useless in patient care but over the years I have noticed that I have noticed more and more animals being brought into the hospital.  There is a time and a place for everything and hospitals are not the place for animals.

I first became aware of animal therapy in my hospital years ago when I was seeing a late consult in the ICU and I noted a cat. In the ICU. Sitting on the chest of a fresh open-heart patient. Let’s say I did not react mildly.  I discovered we had no policies and procedures for animals in the hospital. That has since changed, although we have more animals in the hospital than I would like, human and otherwise.

A perusal of the literature suggests that for relieving pain petting a dog may be as efficacious as acupuncture and the proponents trot out the same mechanism of action:

Animal-assisted therapy is a complementary medicine intervention, typically utilizing dogs trained to be obedient, calm, and comforting. Several studies have reported significant pain relief after participating in therapy dog visits. Objective reports of reduced pain and pain-related symptoms are supported by studies measuring decreased catecholamines and increased endorphins in humans receiving friendly dog visits.

I am not going to deny that petting a dog is of benefit. Humans are social animals that like to touch and be touched. I have long thought that the placebo effect of SCAM therapies, such as it is, is a gussied up version of apes grooming each other. Ritual attention is good.  Except “in deference to a million years of evolution, [the SCAM provider] will not attempt to pick fleas off patients; Earthmen are not proud of their ancestors and never invite them ’round to dinner“.  At least I hope so. Nit picking should be reserved for the comments that follow the blog entry.

I have am intrigued by using animals’ sense of smell to help make diagnosis. Most of the time, like using a dog to smell for cancer, I do not see the point outside of proof of concept. It does not seem practical.

However in resource-poor areas, if an animal can be trained to diagnose an infection that could be very helpful.  Some poor dog was trained to smell C. difficile diarrhea (there is an animal I feel very sorry for) and they have trained the African pouch rat to smell MTB. That would be a good use for animals as a reusable and reliable diagnostic tool in those parts of the world that cannot afford modern diagnostic technology.

Other diseases? I recently had a patient who had a companion dog for emotional support and as a seizure-dog who warned him when he was going to seize so he could take preventative valium.

There have been dogs trained to watch for the prodrome of seizures, although my patient’s dog received no such training. What little literature I could find suggests that animals who are not trained are not reliable and may be used to reinforce illness that is not there. Like the cat who could predict death, seizure dogs are most likely an excellent example of confirmation bias.

As is usually the case when someone has a service animal for emotional support, they become quite belligerent when it is suggested that the hospital may not be the best place for a dog or other animal. Words like ‘sue’ and ‘Americans with disability’ get thrown around and the animal stays. Yet another reason I am not a fan of dog owners. Just because you can do something doesn’t mean you should, but consideration for others is not often high on the list of pet owners.*  They do not seem to consider there may be people in the hospital with allergies who cannot simply leave.

Besides dogs and cats, people want to bring all sorts in vermin, er, I mean animals, into the hospital. One of the IC practitioners mentioned that at a prior job they wanted to bring a reptile zoo into a pediatric cancer ward. Good idea, lets bring a Salmonella vector to the most immunoincompetent patients in the hospital.

In Portland they are bringin llamas into hospitals (not mine) and horses (not mine). As some are aware, I am in charge of infection control in my hospitals and I see everything, and I do mean everything, as a potential infection risk. It makes me fun at parties as I can often come up with an infection risk from any human behavior or exposure.

We are all biased by our experience and I am continually impressed with all the weird and unexpected ways people can acquire infections. Murphy was more than an optimist. If something can cause an infection, it will.

There are two infection control issues with animals in the hospital.

First: entertain yourself by watching what people do with their hands. Hands go everywhere and are not always cleaned afterwards. People pet animals but do not clean their hands before, then the next person touches the animal, acquiring whatever organism was on the fur. While I have to foam my hands between each patient, no one ever foams the animal between patients.

While no animal has yet been identified in a hospital outbreak, dogs have been an intermediary for the spread of E. coli urinary tract infections and can be a source for MRSA and fungal infections as well.

Therapy animals have been cultured and they can carry have MRSA and C. difficile. And more:

Visitation of hospitalized people by dogs is becoming commonplace, but little is known about the potential health risks of introducing dogs to healthcare settings. This cross-sectional study evaluated the prevalence of zoonotic agents in a group of 102 visitation dogs from a variety of sources across Ontario. Between May and July 2004, owners were interviewed by a standardized questionnaire while dogs underwent a standardized physical examination. One specimen of faeces, hair-coat brushings and one rectal, aural, nasal, oral and pharyngeal swab were collected from each dog and tested for 18 specific pathogens. All dogs were judged to be in good health. Zoonotic agents were isolated from 80 out of 102 (80%) dogs. The primary pathogen was Clostridium difficile, which was isolated from 58 (58%) faecal specimens. Seventy-one percent (41/58) of these isolates were toxigenic. Extended-spectrum beta-lactamase Escherichia coli was isolated from one (1%) dog, extended-spectrum cephalosporinase E. coli was isolated from three (3%) dogs, and organisms of the genus Salmonella were isolated from three (3%) dogs. Pasteurella multocida or Pasteurella canis was isolated from 29 (29%) oral swabs, and Malassezia pachydermatis was isolated from eight (8%) aural swabs. Giardia antigen was present in the faeces of seven (7%) dogs, while Toxocara canis and Ancylostoma caninum were detected in two (2%) dogs and one (1%) dog, respectively. Methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, Campylobacter spp., Microsporum canis, group A streptococci, Pseudomonas aeruginosa and Cryptosporidium spp. were not detected. Further information is needed before the full implications of these findings for infection control can be assessed properly.

There has yet to be a reported infection transmission or outbreak with a therapy but probably it is because people are not looking.  But given the results of the above, do you really want a dog wandering from room to room in your hospital?

With genetic techniques it is becoming increasingly easy to follow the chain of transmission. Anesthesiologists, as an example, can directly be the source for potential pathogens on the hub of central venous catheters.  It is only a matter of time before these techniques are applied to animals in the hospital.

Not only can animals be the intermediary for human pathogens, they have their own set of pathogens that can spread to humans: Pasteurella and Capnocytophaga being two. I always bear in mind that animals lick their butt and then they lick you. Ick. If I were to scratch my backside and then offer to shake your hand you would likely refuse but probably think nothing of having a dog lick you.

People do not consider animals as a source of infection, in part because the infections are relatively rare, in part because we do not look for them, and in part because who wants to blame the animal?  My favorite healthcare-associated infection, although not hospital acquired, was a patient who let her cat sleep in her dialysis bag warmer and she developed CAPD peritonitis with Pasteurella. And I can go on and on. And on. And on. About all the curious ways in which humans acquire infections from animals

To compound the problem, with the widespread use of veterinary antibiotics, it is of no surprise that pets and animals are a source for antibiotic-resistant bacteria.  I have enough trouble controlling infections from humans, much less adding dogs to the mix.

All of medicine is about the risk vs. the benefit of an intervention. I am particularly paranoid about infections in the hospital given how easily they can be spread.  But simple interventions can stop the spread of infection. It is why I am pushing for autoclaving any animal before we let it in the hospital.

*At some point someone is going to mention the poor behavior of children as a rationalization for lousy pet behavior. Don’t. It is no different than mentioning that since medicine is flawed SCAM is legit. You should know better.

P.S. The world needs more Mark Crislip: I was interviewed for the Skeptiles podcast. I have not heard the final edit, but I mostly rambled about infectious diseases and vaccines.



  • Mark Crislip, MD has been a practicing Infectious Disease specialist in Portland, Oregon, from 1990 to 2023. He has been voted a US News and World Report best US doctor, best ID doctor in Portland Magazine multiple times, has multiple teaching awards and, most importantly,  the ‘Attending Most Likely To Tell It Like It Is’ by the medical residents at his hospital. His multi-media empire can be found at

Posted by Mark Crislip

Mark Crislip, MD has been a practicing Infectious Disease specialist in Portland, Oregon, from 1990 to 2023. He has been voted a US News and World Report best US doctor, best ID doctor in Portland Magazine multiple times, has multiple teaching awards and, most importantly,  the ‘Attending Most Likely To Tell It Like It Is’ by the medical residents at his hospital. His multi-media empire can be found at