W e read with great interest the article by Strenger et al (1) on fecal carriage and intrafamilial spread of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae following colonization at the neonatal ICU (NICU). We agree that only a few data are available on the issue of duration of ESBL gastrointestinal colonization among children. Furthermore, we think that there is substantial parental anxiety concerning these multidrug-resistant strains colonizing young infants discharged from the NICU. We feel data are urgently needed in order to answer appropriate and common questions regarding the duration of colonization and the risk of infection (i.e., urinary tract infection) in carriers of these isolates.Due to previous detection of ESBL+ isolates in our NICU at the Western Galilee Hospital in Israel, we carry out a weekly screen of the entire NICU population for rectal carriage of ESBL-producing Enterobacteriaceae in order to detect early colonization and use appropriate isolation (2). Our NICU is a 26-bed tertiary level unit with approximately 550 annual admissions. Use of pulsed-field gel electrophoresis demonstrated a major clone of ESBL+ Klebsiella pneumoniae. In order to better define the duration of colonization and the risk factors for infection in carriers of ESBL+ strains, we conducted a retrospective cohort study of infants discharged from the NICU carrying ESBL+ isolates between the years 2007 and 2011. Rectal swabs were taken repeatedly from participants in 2011-2012 and demographic and clinical data collected. Isolates were compared by species and antimicrobial susceptibility. Identification of ESBL+ strains was performed according to the Clinical and Laboratory Standards Institute guidelines (3). The study was approved by the Institutional Review Board of Western Galilee Hospital and Israeli Ministry of Health.Of 210 children acquiring ESBL colonization in the NICU, 65 (31%) infants 1-51 months old (median 25 mo) participated with at least one rectal swab; 63% had two or more swabs taken. The infants' mean gestational age, birth weight, and duration of stay in the NICU were 31 weeks, 1620 g, and 36 days, respectively. The participating infants were colonized with K. pneumoniae (62/65, 95%) and Escherichia coli (3/65, 5%). Mean time to acquisition of ESBL+ strain was 16 days. Rectal colonization was observed to the age of 6 months. Infants older than 6 months were not colonized. Although almost half of the infants (31/65, 48%) were readmitted, none were infected with ESBL+ strains.Compared with the study by Strenger et al, we demonstrated a shorter duration of colonization with K. pneumoniae, the bacterium most of our infants had carried. The difference in duration might be explained by several factors, including difference in the strains, classes of ESBLs, antibiotic pressure discrimination with all the three scores (PRISM, PIM, and PIM-2) but calibration was good with only PRISM and PIM-2. The standardized mortality ratio (SMR) was more than 1 with all the three models. The mortality rate ...