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




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.


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.


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.

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We thank all of the participating pregnant women and infants; all the midwives at the Department of Obstetrics, Stavanger University Hospital, especially Liv Ingunn Nevland, for recruiting the participants, secretary Wenche Digranes at the Pediatric Department, Stavanger University Hospital, Ragnhild Omholt and Kirsti Gummedal at the Department of Medical Microbiology, Stavanger University Hospital, biostatistician Geir Egil Eide, Centre for Clinical Research, Haukeland University Hospital, Bergen, and the Norwegian Reference Center for Detection of Antimicrobial Resistance, University Hospital of North Norway, for their support. This work was partly funded by a grant from NORM surveillance program for antimicrobial resistance in human pathogens.

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Correspondence to S Rettedal.

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This work was presented as a poster at the 31st Annual Meeting of the Nordic Society of Clinical Microbiology and Infectious Diseases, Bergen, Norway 2014.

Supplementary Information accompanies the paper on the Journal of Perinatology website .

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Rettedal, S., Löhr, I., Bernhoff, E. et al. Extended-spectrum β-lactamase-producing Enterobacteriaceae among pregnant women in Norway: prevalence and maternal–neonatal transmission. J Perinatol 35, 907–912 (2015).

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