Multiresistant CTX-M-15 ESBL-producing Escherichia coli in southern Sweden: Description of an outbreak.

An outbreak caused by a multiresistant Escherichia coli producing CTX-M-15 ESBL occurred during autumn 2005 and spring 2006 in Kristianstad, a town in southern Sweden. The outbreak comprised 27 cases and was related to an infectious diseases ward and a neighbouring long-term care facility. Our primary objective was to investigate the epidemiology in order to control the outbreak. In addition, we studied the time of carriage of multiresistant ESBL-producing Escherichia coli by follow-up samples and measured the frequency of carriage of ESBL-producing bacteria in the patient population admitted to the infectious diseases ward during autumn 2006. The outbreak described is one of the first caused by ESBL-producing Escherichia coli in Sweden. The source of the outbreak was not found. Infection control measures were reinforced in the outbreak situation, and epidemiological and microbiological methods, including PFGE typing, were used for analysis. The carriage time of multiresistant Escherichia coli was longer in several of the affected patients than has previously been reported. The longest carriage time to date is 33 months. This demonstrates the risk for new outbreaks unless strict infection control measures are implemented. Among the patients admitted to the ward during autumn 2006, 2.5% carried ESBL-producing enterobacteria.

The DiversiLab system versus pulsed-field gel electrophoresis: characterisation of extended spectrum ß-lactamase producing Escherichia coli and Klebsiella pneumoniae.

Fast and reliable epidemiological typing methods for identifying outbreaks and epidemic strains of extended spectrum ß-lactamase (ESBL) producing Enterobacteriaceae are urgently needed. The DiversiLab system (DL) has been proposed for these purposes. We compared DL to pulsed-field gel electrophoresis (PFGE) on a national collection of ESBL-producing Escherichia coli (n=258; of which 226 isolates were typeable with PFGE) and Klebsiella pneumoniae (n=48) isolated in 2007. For E. coli the Wallace coefficients showed that the probability of two isolates of the same DL type having the same PFGE type was only 19.8% and the probability of two isolates of the same PFGE type having the same DL type was 90.4%. For K. pneumoniae the Wallace coefficients showed that the probability of two isolates of the same DL type having the same PFGE type was 100% and the probability of two isolates of the same PFGE type having the same DL type was 79%, indicating that for this K. pneumoniae strain collection DL was slightly more discriminatory. Only four of 48 isolates had discordant results with the two methods. In E. coli 42% of the isolates were sequence type 131 and these isolates were related at >95% similarity with DL and at ≥60% similarity with PFGE. In summary, for E. coli DL performed well in identifying isolates related by PFGE, but overestimated the genetic relatedness in the studied collection. This indicates that DL could be a primary screening method for excluding unrelated isolates. Isolates shown to be related must be confirmed with a more discriminatory method. For K. pneumoniae, DL discriminated well but overestimated the diversity of the isolates compared to PFGE, assuming a risk of missing possible genetic relatedness.