Local outbreak of Clostridioides difficile PCR-Ribotype 018 investigated by multi locus variable number tandem repeat analysis, whole genome multi locus sequence typing and core genome single nucleotide polymorphism typing.

The prevalence of Clostridioides difficile PCR-ribotype (RT) 018 is low in Europe but variations are observed across countries. We report here the first RT 018-related outbreak in France that took place in 4 geriatric units (GU) in Strasbourg, France. From January to December 2017, 38 patients were diagnosed with C. difficile infection (CDI). Strains were first characterized by PCR ribotyping: 19 out of 38 (50%) strains belonged to RT 018. These strains as well as 12 RT 018 isolated in other French healthcare facilities and 2 strains of RT 018 isolated in the GU in 2015 were characterized by multi locus variable-number tandem repeat (VNTR) analysis (MLVA), whole genome multi locus sequence typing (wgMLST) and core genome single nucleotide polymorphism typing (cgSNP). The MLVA indicated that 15 out of 19 epidemic strains of RT 018 were included in 2 Clonal Complexes (CC). Four RT 018 strains from the outbreak did not belong to the CC. The wgMLST and cgSNP typing analysis revealed a single CC that included 19 strains from the geriatric unit (17 from GU in 2017 and 2 from GU in 2015) and 4 strains (33%) from other healthcare facilities (HCF). Our results suggest that a specific RT 018 clone has spread in the geriatric unit and has evolved slowly over time. MLVA, wgMLST and cgSNP typing results provided fairly consistent information but wgMLST and cgSNP typing better separated epidemic strains from non-epidemic strains. Compared to wgMLST, the cgSNP typing did not provide additional information.

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