October 05, 2018
3 min read

Antiseptic prevents therapy dogs from spreading MRSA to pediatric cancer patients

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Kathryn Dalton
Kathryn Dalton

SAN FRANCISCO — Researchers found that a low-cost cleaning procedure could prevent therapy dogs from spreading MRSA among pediatric cancer patients — presenting a possible solution to the danger that therapy animals pose to at-risk patients.

The decolonization procedure involved washing dogs with chlorohexidine-based shampoo before their first visit with patients and cleaning their fur with chlorohexidine wipes every 5 to 10 minutes during sessions.

Kathryn Dalton, VMD, MPH, a PhD candidate in the department of environmental health and engineering at Johns Hopkins Bloomberg School of Public Health, and colleagues evaluated the intervention in children receiving outpatient cancer treatment at Johns Hopkins Children’s Center and reported that it reduced the number of children and dogs who became MRSA carriers following visits.

The study was conducted during 13 group therapy visits by dogs — six sessions in which the dogs underwent decolonization and seven control sessions. During visits, children have close contact with the dogs, petting, hugging, kissing and playing fetch with them, the researchers said.

hospital therapy dog 
Washing therapy dogs with chlorhexidine-based shampoo and cleaning them frequently with chlorohexidine wipes every 5 to 10 minutes lessened the chance that the dogs would spread MRSA among pediatric cancer patients.
Source: Adobe Stock

The pilot study included 45 patients aged 2 to 20 years being treated for cancer and four therapy dogs. All children and dogs were tested for MRSA carriage before and after visits. Dalton and colleagues hypothesized that the dogs — as an “intermediary fomite” — facilitated transmission from MRSA-positive patients to noncolonized patients.

They found that in control groups, patients who interacted closely with therapy dogs were six times more likely to become MRSA carriers than those who did not. However, when dogs were decolonized according to the procedure, the risk among patients was the same regardless of their interaction with the dogs.

“It essentially removed the dog from the equation,” Dalton said at a news conference during IDWeek.

Clinicians requested study

According to the CDC, around 33% of people carry Staphylococcus bacteria in their nose — usually without becoming sick — and 2% carry MRSA. Companion animals also are known to carry MRSA, and there has been at least some apprehension about the potential infection risk that therapy dogs pose for patients, especially those with weakened immune systems, such as patients being treated for cancer, who are at an increased risk for serious MRSA infections.

Dalton said the study was initiated at the request of practicing physicians at the hospital who were concerned about the risk. Rather than pointing out a problem that was assumed to exist, Chris Nyquist, MD, MPH/MSPH, a professor of pediatrics at the University of Colorado School of Medicine, said the study provides a starting point for a conversation about how to balance the safety of patients and the benefits that therapy dogs provide.


In addition to their primary findings, Dalton and colleagues reported that patients experienced positive physiological and mental health outcomes: Interacting with the dogs lowered their blood pressure and heart rate and improved their mental health.

Nyquist, who was not involved in the study, is the medical director for infection prevention and control at Children’s Hospital Colorado, which has had a long-standing pet therapy program.

“This study really speaks to me in an important way,” she said at the news conference. “We have limited [therapy dogs] [for] our oncology patients because of concerns about transmission of infection, which is really sad because they’re the patients who are in the hospital the longest. We also don’t allow dogs into the operating room. This study really brings a method for us to expand the ability for pet therapy dogs potentially to areas where they haven’t been able to go.”

Overall, regardless of the level of interaction with the dogs, Dalton said the intervention led to a 90% decreased risk for MRSA colonization in patients. She said the research team has secured additional funding to conduct a larger study in multiple hospitals to explore whether the intervention could be used in other settings. And they have already begun testing existing samples from their study and others to look for potential resistance genes.

Who will wash?

If the intervention becomes standard practice, there is some question as to who would clean the dogs. During the study, Dalton said handlers took care of the previsit shampooing and she performed the wiping.

“This is something that could feasibly be done either by the dog handler or hospital staff,” she said.

Study author Meghan Davis, PhD, DVM, MPH, assistant professor in the department of environmental health and engineering at Johns Hopkins Bloomberg School of Public Health, said companion animals tend to carry strains of Staphylococcus aureus, including MRSA, that are distributed in humans, typically picking them up from owners or other people they interact with closely.

“If you remove them from the source of human contamination, many times they will clear,” she said at the news conference.

Indeed, Nyquist said humans remain the larger problem when it comes to the spread of MRSA. Recent studies have shown that most hospital privacy curtains are contaminated with MRSA and that the pathogen can be commonly found on hospital floors. The CDC recommends standard precautions to control the spread of MRSA in hospitals in most instances, including routine hand-washing.

“This is a way to wash the dogs,” Nyquist said. – by Gerard Gallagher


Dalton K, et al. Abstract 160. Presented at: IDWeek; Oct. 3-7, 2018; San Francisco.

Disclosures: Dalton, Davis and Nyquist report no relevant financial disclosures.