Genomic Epidemiology of Clostridioides difficile Infection: A cgMLST Analysis.

AIM: To characterise the genomic epidemiology of Clostridioides difficile infection (CDI) at Letterkenny University Hospital (LUH) using core-genome Multi Locus Sequence Typing (cgMLST), quantify true nosocomial transmission, distinguish relapse from reinfection, and examine the relationship between CDI patterns and institutional antimicrobial consumption. METHODS: In 2023 and 2024, 1,510 and 1,754 stool samples were screened, respectively for suspected CDI. GDH screening was positive in 153 (10.1%) and 226 (12.9%) with toxin EIA detecting active toxin in 86 (56.2%) and 106 (46.9%), respectively. PCR identified toxin genes in a further 44 (65%) and 72 (60%) of toxin-negative GDH-positive samples. Of these, 117, toxin-positive isolates from 94 patients underwent whole-genome sequencing and cgMLST. Molecular clusters were defined as ≤2 allelic differences, and epidemiological linkage required shared ward location and overlapping admission periods. National antimicrobial-use deciles were reviewed for CDI-associated agents. RESULTS: cgMLST identified 28 sequence types, with ST11 predominating (19, 16.2%). Of 48 clusters, only one represented confirmed nosocomial transmission. Recurrent CDI occurred in 10 out of 94 (11%), with 90% representing molecular relapse. LUH ranked among the highest national consumers of CDI-associated antimicrobials. DISCUSSION: CDI at LUH is driven primarily by endogenous activation of community-acquired strains rather than hospital transmission. High-risk antimicrobial use is the key modifiable driver, highlighting the need for strengthened antimicrobial stewardship supported by ongoing WGS surveillance.