Persistence of OXA-48-producing ST-22 Citrobacter freundii in patients and the hospital environment, Paris, France, 2016 to 2022.

In 2016-2019, hospital A's haematology ward experienced an outbreak of OXA-48-producing ST-22 Citrobacter freundii strains, with toilets identified as source of transmission. Between 2020 and 2022, 28 strains of OXA-48-producing ST-22 C. freundii were isolated on other wards. This study aimed to determine whether all OXA-48-producing ST-22 C. freundii strains belonged to the same clone and to investigate the persistence of this clone using whole genome sequencing. OXA-48-producing ST-22 C. freundii strains collected from patients (n = 33) and from the hospital environment (n = 20) of seven wards were sequenced using Illumina technology and clonal relationships were determined using single nucleotide polymorphism (SNP). Phylogenetic analyses were performed on 53 strains from hospital A and on 240 epidemiologically unrelated carbapenem-resistant ST-22 C. freundii isolated from elsewhere in France. SNP analysis suggested long-lasting persistence of the same clone for more than 6 years. Phylogenetic analysis showed that 52 of 53 strains isolated in hospital A belonged to the same cluster and were different from the 240 epidemiologically unrelated C. freundii ST-22. Our data suggest that this clone can persist in hospital environments for years, representing a risk for hospital-acquired infections and outbreaks. Reservoir management is essential to prevent further transmission.