Clinical significance of extended-spectrum beta-lactamases.

Extended-spectrum beta-lactamases (ESBLs) have now been described in many hospitals worldwide. While they have been detected in many pathogenic gram-negative bacteria, they are particularly prevalent in Klebsiella isolates. Known risk factors for colonization and/or infection with organisms harboring these enzymes include admission to an intensive care unit, recent surgery, instrumentation, prolonged hospital stay and antibiotic exposure, especially exposure to extended-spectrum beta-lactam agents. In this report three recent epidemics from the USA will be described in which the role of selective antibiotic pressure seems clear. Data from two hospital epidemics, one from New York and another from Stanford, California, will be reviewed briefly. In addition, recent studies describing the spread of extended-spectrum beta-lactamases among nursing home patients in Chicago, Illinois, will be outlined. The limited data available on treatment options for patients infected with ESBL-containing strains will be reviewed, focusing on the activity of piperacillin/tazobactam and imipenem against these otherwise broadly resistant strains. Lastly, attempts to control these organisms, including infection control measures and selective bowel decontamination, will be reviewed.