Genetically diverse, community-based sources of Clostridium difficile may play a larger role in nosocomial transmission than previously thought, a study found.
Researchers performed whole-genome sequencing on isolates obtained from patients with C. difficile infection identified through health care or community settings in Oxfordshire, U.K., from September 2007 through March 2011. The researchers looked at single-nucleotide variants (SNVs) between the isolates. Genetic relationship was defined as ≤2 SNVs between the 2 isolates.
Results appeared in the Sept. 26 New England Journal of Medicine.
Of 957 sequenced isolates from patients with C. difficile infection, 333 (35%) were genetically related to at least 1 isolate from a previous case, and 428 (45%) had more than 10 SNVs. Of the 333 patients with genetically related isolates, 126 (38%) had ward contact with a previous genetically related case, 5 (2%) were linked only by possible ward-based contamination after the discharge or recovery of an infectious patient, 29 (9%) shared time in the same hospital but were never on the same ward, and 21 (6%) had both ward contamination and hospital-wide contact.
However, the remaining 152 patients (46%) had no hospital-based contact. Of these patients, 15 (10%) were patients at the same general medical practice, and 17 (11%) lived in the same postal-code district. Overall, 120 patients (36%) had no hospital or community contact with a previous genetically related case, and when researchers looked back at unlimited infectious, incubation, and ward-contamination periods, 68 patients (20%) still had no hospital or community contact.
The researchers noted that since 45% of cases had sufficient genetic diversity to represent transmission originating from sources other than the cases that were included in the study, and since distinct subtypes of infection continued to be identified throughout the study, there may be a considerable reservoir of C. difficile in the community.
The authors noted several changes to antibiotic prescribing habits across the U.K. during the study period, including the reduction in use of fluoroquinolones and cephalosporins.
“The incidence of genetically distinct C. difficile cases was similar to that of genetically related cases,” the authors wrote. “This finding suggests that interventions to reduce susceptibility to disease in exposed patients (e.g., changes in the use of antibiotics or specific types of antibiotics), rather than just to reduce transmission of C. difficile from symptomatic patients, might have played a major role in reductions in the incidence of C. difficile infection in the region during the past 5 years.”
An accompanying editorial noted that the study challenges the idea that symptomatic patients in hospitals account for most C. difficile transmission and infection.
“The findings will not alter recommendations that basic control measures are essential,” the editorial stated. “Infrequent transmission from symptomatic patients in the study hospitals may in fact attest to the effectiveness of well-implemented control programs. The major implication of the study is that control of C. difficile will require that we move beyond the usual suspects (symptomatic patients in hospitals).”