Whole-genome sequencing improves discrimination of relapse from reinfection and identifies transmission events among patients with recurrent Clostridium difficile infections.

Summary Background Recurrent Clostridium difficile infection (CDI) represents a significant healthcare challenge. Patients may suffer multiple episodes of CDI with the index strain (relapse) or become infected by another strain acquired nosocomially (reinfection). Aim We aimed to characterize C. difficile isolates causing recurrent CDI at a tertiary referral hospital by whole-genome sequencing (WGS) to assess strain similarities at the highest level of genetic resolution and accurately detect relapse, reinfection, and putative strain transmission events. Methods An 18-month prospective study of recurrent CDI was undertaken. Clostridium difficile was cultured from stool samples collected longitudinally from any patients suffering ≥2 clinically defined CDI episodes. Patient demographics and clinical data were recorded, and strain relatedness investigated by both polymerase chain reaction (PCR)-based ribotyping and WGS. Findings Nineteen patients were identified with ≥2 clinically defined CDI episodes who cumulatively suffered 39 recurring CDI episodes (58 total episodes). Patients had a median length of stay (LOS) of 144 days and experienced between two and seven CDI episodes. Ribotyping indicated 27 apparent same-strain relapses, five reinfections and the predominance of ribotypes 078 (ST-11) and 020 (ST-2). WGS allowed characterization of relapse with increased certainty and identified emergent within-strain single nucleotide variants (SNVs) with potential functional impact on diverse genes. Shared ribotypes among 14 patients with recurrent CDI suggested 10 possible patient-to-patient transmission events. However, WGS revealed greater diversity at the sub-ribotype level, excluding all but four transmission events. Conclusion WGS exhibits several advantages over PCR-based ribotyping in terms of its ability to distinguish relapse from reinfection, to identify patient-to-patient transmission events, and to exact fine structure characterization of recurrent CDI epidemiology. This offers the potential for more focused infection prevention strategies to eliminate strain transmission among patients with recurrent CDI.