Objectives: As part of the ongoing national Clostridium difficile Antimicrobial Resistance Surveillance (CDARS) study, we sought to describe the molecular epidemiology of C. difficile infection (CDI) in the Australian healthcare and community settings in 2015.
Methods: Ten laboratories across Australia; one private and one public laboratory from five states submitted isolates of C. difficile or PCR positive stool samples during two collection periods for summer/autumn (February-March; CDARS phase 4) and winter/spring (August-September/ CDARS phase 5) 2015. C. difficile was characterized by PCR for toxin genes and ribotyping.
Results: A total of 307 eligible samples were received, of which 45% and 47% of the total collected were submitted by private laboratories from the two collection periods, respectively. From these samples, 285 isolates of C. difficile [WA (n=58), VIC (n= 55), SA (n=53), QLD (n=61) and NSW (n=56)] were recovered. PCR ribotyping yielded 71 different ribotypes (RTs) and 76% of strains (218/285) were assigned to 1 of 30 internationally recognised RTs. The most prevalent RTs were 014/020 (31%, n=88), 056 (8%, n=22) and 002 (7%, n=21). Epidemic RTs 027 (n=1), 078 (n=3) and the recently emerged RT251 (n=1) were found, as well as a single isolate of RT017. The vast majority (88%) of strains were positive for the major toxin genes tcdA/B, of which 4% (n=12) were also positive for genes encoding binary toxin (cdtA/B) and 7% (n=20) were non-toxigenic strains. Similar distributions were seen for RTs between states, although phase 5 appeared to have increased numbers of RTs 056 (n= 5 vs. 17) and 002 (n=6 vs. 15).
Conclusions: A heterogeneous C. difficile strain population was identified in Australia. RT014/020 was the most prevalent C. difficile strain found in humans with CDI. This successful lineage is also the most common RT in pigs in Australia, suggesting a potential zoonotic reservoir for human CDI. Continuous surveillance of circulating C. difficile strains is important for tracking of prominent and emerging strain types.