Faecal carriage of extended-spectrum β-lactamase-producing Enterobacteriaceae is common 12 months after infection and is related to strain factors.

We aimed to determine the duration of faecal carriage of extended-spectrum β-lactamase (ESBL) -producing Enterobacteriaceae (EPE) in patients with clinical infection caused by an EPE, to study host strains during carriage, and to identify factors associated with prolonged carriage. Patients (n = 61) were followed with faecal samples and questionnaires about antimicrobial treatment and risk factors for EPE, 1, 3, 6 and 12 months after EPE infection. The EPE isolates were subjected to ESBL genotyping, epidemiological typing with pulsed-field gel electrophoresis and PCR-based replicon typing. Escherichia coli isolates were analysed with PCR for phylogrouping, detection of pabB (ST131) and virulence content. Patient-related and strain-related variables were compared for carriers and non-carriers at 12 months. Carriage of EPE was observed in 51 of 61 (84%) patients after 1 month, 36 of 61 (66%) after 3 months, 31 of 61 (55%) after 6 months and 26 of 61 (43%) after 12 months. Of the 26 carriers at 12 months, five had previous negative samples. In 17 of 61 patients, ESBL was found in a new bacterial species and/or strain during carriage. Among E. coli, 14 of 49 belonged to the international clone ST131. Phylogroup B2 and CTX-M-gr.-9 were associated with being carriers at 12 months (OR 4.3, 95% CI 1.1-16.3 and OR 6.4, 95% CI 1.3-30.9, respectively). In conclusion, EPE carriage is common 12 months after infection and persisting carriage may be associated with E. coli phylogroup B2 and CTX-M-gr.-9. The host strain frequently changes throughout carriage and negative samples do not imply eliminated carriage.