High clonal diversity of ESBL-producing Klebsiella pneumoniae isolates from clinical samples in a non-outbreak situation. A cohort study.

Background: Klebsiella pneumoniae has been responsible for a large number of clonal hospital outbreaks. However, some epidemiological changes have been observed since the emergence of CTX-M enzymes in K. pneumoniae. Aim: To analyse the transmission dynamics of Extended Spectrum beta-Lactamase-producing Klebsiella pneumoniae (ESBL-Kp) in an acute care hospital. Methods: In 2015 a prospective cohort study was conducted. All new consecutive adult patients with ESBL-Kp isolates in all clinical samples were included. Patients with a previous known infection/colonization by ESBL-Kp and patients in high risk areas (e.g., intensive care units) were excluded. Cross-transmission was defined as the carriage of a clonally-related ESBL-Kp between newly diagnosed patients who shared the same ward for >/=48 h with another case, within a maximum time window of 4 weeks. ESBL-production was confirmed using the double-disk diffusion method and PCR. Clonal relationships were investigated by rep-PCR and multilocus sequence typing (MLST). Results: Sixty ESBL-Kp isolates from 60 patients were included and analysed. Infections and colonizations were classified as hospital-acquired (52%), healthcare-related (40%) or community-acquired (8%).High genetic diversity was detected. When epidemiological clinical data were combined with the rep-PCR, the patterns identified did not show any cases of cross-transmission. ESBL-Kp were detected in 12.5% of environmental samples. No clonal relationship could be established between environmental reservoirs and patients. The genetic mechanism detected in all strains was associated with bla CTX-M genes, and 97% were CTX-M-15. Conclusions: The dynamics of ESBL-K. pneumoniae isolated in our setting could not be explained by clonal transmission from an index patient. A polyclonal spread of ESBL-Kp was identified.