Clostridium difficile

Reports of community-associated Clostridium difficile infections (CA-CDIs) in humans have been on the rise in Canada, the United States, and Europe over the last several years. The goal of this prospective study was to assess the risk for C difficile transmission from human patients with CDI to their household contacts, both humans and pets.  

The study included 51 human outpatients with 67 human and 15 pet household contacts. Stool samples or rectal swabs were obtained at the baseline home visit after diagnosis and monthly for 4 months. C difficile-positive samples were tested to determine if isolates were toxigenic and to assess strain relatedness. 

Of the human patients, 29/51 (56.8%) tested positive for toxigenic C difficile during at least one follow-up visit. Among the human household contacts, 9/67 (13.4%) tested positive; 4 of these contacts were initially culture-negative, then converted to positive on subsequent visits. One contact had an isolate indistinguishable from the index case, which indicated probable transmission. Five human contacts were culture positive at the baseline visit, which made directionality of transmission indeterminable. 

One culture-positive human contact developed symptomatic CDI. Four pet contacts (2 dogs, 2 cats) were culture positive, with 1 cat positive at baseline. Testing showed all 4 isolates from the pets were indistinguishable from those of the patient. All pets remained subclinically affected.  

The authors suggested that transmission from outpatients with CDI to human and pet household contacts could contribute to an ecologic reservoir from which additional CA-CDIs may develop.

Global Commentary

Clostridium difficile has previously been identified in fecal samples from both dogs and cats, but CDIs leading to diarrheal disease are not a recognized clinical problem in either species. However, pets may serve as a reservoir for human CDI. 

This study, although rather small and selective (total number of CDIs at the same hospital during the same time period: 1367), showed probable C difficile transmission from human CDI patients to a cat and 2 dogs and a possible transmission to an additional cat. Such transmission was suspected in previous studies; however, this is the first study that used pulsed-field gel electrophoresis, a method for molecular typing, to determine relatedness of C difficile isolates and thus likelihood of transmission between the human patient and the pet contact.  

It should be noted that total transmission (probable plus possible) to pet contacts (26.7%) far outreached total transmission to human contacts (9%). However, these findings should be considered with caution. Other factors (eg, abundance of the organisms in feces, duration of shedding) may play a more important role than simple presence in retransmission of C difficile to a human patient.

—Jörg Steiner, MedVet, DrMedVet, PhD, DACVIM, DECVIM-CA, AGAF, Texas A&M University, United States