Infrequent intra-household transmission of Clostridioides difficile between pet owners and their pets

Objective Companion animals have been shown to carry Clostridioides difficile strains that are similar or identical to strains found in people, and a small number of studies have shown that pets carry genetically identical C. difficile isolates as their owners, suggesting interspecies transmission. However, the directionality of transmission is ultimately unknown, and the frequency with which animals acquire C. difficile following their owners' infection is unclear. The goal of this study was to assess how often pets belonging to people with C. difficile infection carry genetically related C. difficile isolates. Methods We enrolled pet owners from two medical institutions (University of Pennsylvania Health System (UPHS) and The Ohio State University Wexner Medical Center (OSUWMC)) who had diarrhea with or without positive C. difficile assays and tested their feces and their pets' feces for C. difficile using both anaerobic culture and PCR assays. When microorganisms were obtained from both the owner and pet and had the same toxin profile or ribotype, isolates underwent genomic sequencing. Results Fecal samples were obtained from a total of 59 humans, 72 dogs, and 9 cats, representing 47 complete households (i.e., where a sample was available from the owner and at least one pet). Of these, C. difficile was detected in 30 humans, 10 dogs, and 0 cats. There were only two households where C. difficile was detected in both the owner and pet. In one of these households, the C. difficile isolates were of different toxin profiles/ribotypes (A+/B+ / RT 499 from the owner, A-/B- / RT PR22386 from the dog). In the other household, the isolates were genetically identical (1 SNP difference). Interestingly, the dog from this household had recently received a course of antibiotics (cefpodoxime and metronidazole). Conclusions Our findings suggest that interspecies transmission of C. difficile occurs infrequently in households with human C. difficile infections