Extended-spectrum beta-lactamase-producing Klebsiella pneumoniae in a neonatal intensive care unit: risk factors for infection and colonization.

An outbreak of extended spectrum beta-lactamase-producing Klebsiella pneumoniae (ESBLKp) infections in a neonatal intensive care unit (NICU) prompted a prospective investigation of colonization and infection with this pathogen. From August 1, 1997 to May 30, 1999, neonates admitted to the NICU for more than 24 h were screened for ESBLKp acquisition. Neonatal gastrointestinal screening was performed by means of faecal sampling within 48 h of admission and then weekly until discharge. Isolates were typed using pulsed-field gel electrophoresis (PFGE). Time-dependent proportional hazard models were used to identify independent effects of invasive procedures and antimicrobials after controlling for duration of stay at the NICU. During the study period, 464 neonates were admitted and 383 were regularly screened. Infections occurred in 13 (3.4%) neonates and 206 (53.8%) became colonized. Independent risk factors for colonization during the first nine days in the NICU were the antimicrobial combination cephalosporin plus aminoglycoside [hazard rate (HR)=4.60; 95% CI: 1.48-14.31], and each NICU-day was associated with a 26% increase in the hazard rate for colonization (HR=1.26; 95% CI: 1.16-1.37). Previous colonization (HR=5.19; 95% CI: 1.58-17.08) and central vascular catheter use (HR=13.89; 95% CI: 2.71-71.3) were independent risk factors for infection. In an outbreak setting the proportion of neonates colonized with ESBLKp was observed to increase with the duration of stay and antimicrobial use, and once colonized, infants exposed to invasive devices may become infected.