Maternal Carriage in Late-Onset Group B Streptococcus Disease, Italy

We retrospectively investigated mother-to-infant transmission of group B Streptococcus (GBS) in 98 cases of late-onset disease reported during 2007-2018 by a network in Italy. Mothers with full assessment of vaginal/rectal carriage tested at prenatal screening (APS) and at time of late onset (ATLO) were included. Thirty-three mothers (33.7%) were never GBS colonized; 65 (66.3%) were vaginal/rectal colonized, of which 36 (36.7%) were persistently colonized. Mothers with vaginal/rectal colonization ATLO had high rates of GBS bacteriuria (33.9%) and positive breast milk culture (27.5%). GBS strains from mother-infant pairs were serotype III and possessed the surface protein antigen Rib. All but 1 strain belonged to clonal complex 17. GBS strains from 4 mother-infant pairs were indistinguishable through pulsed-field gel electrophoresis. At least two thirds of late-onset cases are transmitted from mothers, who often have vaginal/rectal carriage, positive breast milk culture, or GBS bacteriuria, which suggests heavy maternal colonization.

Automated summary

Retrospective investigation in Italy from 2007 to 2018 found that at least two thirds of late-onset GBS cases are transmitted from mothers, who often have high maternal colonization such as vaginal/rectal carriage, positive breast milk culture, or GBS bacteriuria. The GBS strains from mother-infant pairs were mainly serotype III belonging to clonal complex 17, with some strains indistinguishable through pulsed-field gel electrophoresis.