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J Pediatr. 2013 Oct;163(4):1099-104.e1. doi: 10.1016/j.jpeds.2013.05.064. Epub 2013 Jul 15.

Group B streptococcal colonization in 160 mother-baby pairs: a prospective cohort study.

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Neonatal Intensive Care Unit, Polyclinic University Hospital, Modena, Italy. Electronic address:



To identify the source of postnatal colonization with group B Streptococcus (GBS) and to evaluate the impact of intrapartum antibiotic prophylaxis (IAP) administration in newborn infant transmission.


A prospective, longitudinal study evaluated GBS colonization in 160 mother-baby pairs. Specimens were collected from the time of delivery to 8 weeks post-partum, from rectum, vagina, and milk of mothers, and from throat and rectum of neonates. Women were grouped according to their GBS status at discharge from the hospital: culture-positive carriers (n = 83), culture-negative carriers (n = 26), and noncarriers (n = 51). Newborns were considered colonized if GBS was yielded from at least 1 site.


A total of 35 (21.9%) neonates were colonized; 30 were born to culture-positive carriers, 2 to culture-negative carriers, and 3 to noncarriers. Infants of culture-positive carriers exposed to IAP were less likely to be colonized (15/57 vs 15/26, P = .01), or heavily colonized, (7/57 vs 9/26, P = .04). Of all newborns, those exposed to IAP and discharged GBS-free from hospital, often became colonized subsequently (12/57 vs 1/26, P = .09). Molecular typing analysis (available for 30 of 32 carrier mothers and their infants) confirmed an identical strain of GBS in all mother-baby pairs. Six of 83 culture-positive carrier mothers had a positive milk culture. Their respective neonates all were heavily colonized.


Newborns exposed to IAP and GBS-free at hospital discharge subsequently acquire GBS from their mothers. Culture-positive milk is associated with heavy neonatal colonization.


EOD; Early-onset disease; GBS; Group B Streptococcus; IAP; Intrapartum antibiotic prophylaxis; LOD; Late-onset disease; PFGE; Pulsed field gel electrophoresis; THB; Todd-Hewitt broth

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