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 beta-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.