To Pet or Not: Canine Assisted Therapy and the Risk of Clostridium difficile

Background: Clostridium difficile (CD) is a gram-positive anaerobic bacillus that increases economic burden, worsens patient outcome and is associated with up to 15% mortality.  Animal assisted therapy (AAT) is becoming common in healthcare facilities. Many studies report on the effectiveness of AAT on therapeutic interventions. However, little is known about the prevalence and risk of CD infections associated with these programs. The risk of disease transmission is a concern encountered in any AAT program.

Objective: This study is to assess the potential risk of transmissibility of CD during canine assisted therapy (CAT) sessions and determine the interspecies relationship among present canine CD isolates.  

Methods: A study was conducted at a tertiary care center from July 2007-October 2009.  Inclusion criteria were all hospitalized patients who had at least one CAT session.  All CAT canines complied with hospital and CDC guidelines on animal hospital visitation.  Enrolled patients were cross-referenced to lists of CD positive patients as provided by hospital infection control.  Stool cultures from each canine were drawn quarterly during the study period. Canines that tested positive were not permitted to continue with patient visitation until treated, cleared by their own veterinarian or had three consecutive negative stool cultures.  The genomic content of positive canine CD isolates was analyzed by pulse field gel electrophoresis (PFGE) to obtain genetic profiles.

Results: 1242 patients were enrolled and were visited by 46 canines.  717 patients were adults and 525 were children, with a total of 3953 visits averaging of 3.18 visits per patient. 202 (15.8%) patients were in critical care units.  No study patients were found to have positive CD culture results during the study period, as documented by hospital infection control.  15 canines had positive stool samples at least one time. Preliminary analysis of 4 canine isolates is presented in Table 1. Isolate type NAP4 shows similarity to the virulent and common human strain, NAP1, suggesting a potential risk of interspecies transmissibility. The remaining CD isolates microarray analysis is still in progress.

Table1: PFGE of canine C difficile isolates
Canine	C difficile isolate type	Comments
1	22801-08: unnamed	> 80% similarity to equine and other nonhuman isolates
2	22221-08: NAP4	Similar to human isolate (NAP1 strain) with toxins A, B, binary
3,4	20155-08 & 22805-08: unnamed	No information in reference isolates

Conclusions: There were no CD infections in enrolled patients during the study period.  This attests to the safety of AAT when complying with CDC guidelines.  There were, however, some canines with positive CD stool cultures.  The preliminary microarray analysis of canine CD genomes shows large diversity.  The presence of similar isolates in different species suggests adaptation and raises the question of interspecies transmission, warranting further research.