Extended-spectrum β-lactamase-producing Enterobacteriaceae among pregnant women in Norway: prevalence and maternal–neonatal transmission

Objective:to study (i) the prevalence and risk factors for carriage of extended-spectrum β-lactamase-producing enterobacteriaceae (esbl-e) in pregnant women, (ii) the maternal–neonatal transmission rate of esbl-e at birth and (iii) the prevalence of esbl-e in expressed breast milk of colonized mothers.study design:in this cross-sectional, population-based study with case follow-up on maternal–neonatal transmission of esbl-e, women were screened for rectal esbl-e colonization at 36 weeks of pregnancy and delivery. possible risk factors for colonization were studied by logistic regression. infants of esbl-e-positive mothers were screened for esbl-e during their first weeks of life. esbl-encoding genes were detected by pcr and clonal relatedness was investigated by pulsed-field gel electrophoreses.results:in total, 26 out of 901 (2.9%) women were colonized by esbl-producing escherichia coli at 36 weeks of pregnancy. one of the women carried an additional esbl klebsiella pneumoniae strain. adjusted for traveling, african or asian nationality was a risk factor for colonization; or=5.62 (2.21, 14.27) (lr-p=0.003). fourteen women remained esbl-e carriers at delivery. esbl-e strains indistinguishable from the strains isolated from their respective mothers were detected in 5 (35.7%) infants during their first days of life (median day 3; range=2 to 8). a total of 146 expressed milk samples were cultured from 25 out of 26 colonized mothers, all were esbl-e negative.conclusions:the prevalence of esbl-e carriage among pregnant women was low in our region, but the high maternal–neonatal transmission rate suggests that colonized mothers represent a substantial risk for infant colonization.