Research Article: Serotype Distribution and Invasive Potential of Group B Streptococcus Isolates Causing Disease in Infants and Colonizing Maternal-Newborn Dyads

Date Published: March 21, 2011

Publisher: Public Library of Science

Author(s): Mashudu Madzivhandila, Peter V. Adrian, Clare L. Cutland, Locadiah Kuwanda, Stephanie J. Schrag, Shabir A. Madhi, Adam Ratner.

Abstract: Serotype-specific polysaccharide based group B streptococcus (GBS) vaccines are being developed. An understanding of the serotype epidemiology associated with maternal colonization and invasive disease in infants is necessary to determine the potential coverage of serotype-specific GBS vaccines.

Colonizing GBS isolates were identified by vaginal swabbing of mothers during active labor and from skin of their newborns post-delivery. Invasive GBS isolates from infants were identified through laboratory-based surveillance. GBS serotyping was done by latex agglutination. Serologically non-typeable isolates were typed by a serotype-specific PCR method. The invasive potential of GBS serotypes associated with sepsis within seven days of birth was evaluated in association to maternal colonizing serotypes.

GBS was identified in 289 (52.4%) newborns born to 551 women with GBS-vaginal colonization and from 113 (5.6%) newborns born to 2,010 mothers in whom GBS was not cultured from vaginal swabs. The serotype distribution among vaginal-colonizing isolates was as follows: III (37.3%), Ia (30.1%), and II (11.3%), V (10.2%), Ib (6.7%) and IV (3.7%). There were no significant differences in serotype distribution between vaginal and newborn colonizing isolates (P = 0.77). Serotype distribution of invasive GBS isolates were significantly different to that of colonizing isolates (P<0.0001). Serotype III was the most common invasive serotype in newborns less than 7 days (57.7%) and in infants 7 to 90 days of age (84.3%; P<0.001). Relative to serotype III, other serotypes showed reduced invasive potential: Ia (0.49; 95%CI 0.31–0.77), II (0.30; 95%CI 0.13–0.67) and V (0.38; 95%CI 0.17–0.83). In South Africa, an anti-GBS vaccine including serotypes Ia, Ib and III has the potential of preventing 74.1%, 85.4% and 98.2% of GBS associated with maternal vaginal-colonization, invasive disease in neonates less than 7 days and invasive disease in infants between 7–90 days of age, respectively.

Partial Text: Group B streptococcus (GBS) has been identified as a major cause of neonatal infection since the 1970s [1], [2]. GBS acquisition by newborns from maternal recto-vaginal colonization is an established risk factor for GBS sepsis within the first 7 days of life [3]. Vertical acquisition of GBS, involving colonization of the skin or mucous membranes, occurs in 15% to 50% of newborns born to GBS colonized mothers. An estimated 1–2% of newborns colonized by GBS develop invasive disease [4], [5].

Overall, GBS was identified from the vagina of 551 (21.5%) of 2 561 mothers and from the skin/mucosal surface of 402 (15.8%) of 2 542 newborns born mothers who were swabbed. GBS was identified in 289 (52.5%) newborns of the 551 mothers who were identified to be vaginally colonized by GBS during labor. In addition, GBS was also identified in a further 113 (5.6%) newborns born to 2,010 mothers in whom GBS was not detected on vaginal swabbing.

To our knowledge this study provides the most in-depth insight of the serotype epidemiology of colonizing isolates in mother-newborn dyads and invasive GBS isolates in an industrializing country setting, and particularly from Africa. Although there are extensive data on maternal colonizing serotype distribution from industrialized countries [17], [18], there are limited data comparing serotype distribution from colonized mothers and their newborns from industrializing countries [19], [20]. The findings from our study are similar to those reported elsewhere, [5], [19], [20] and confirm that maternal GBS vaginal-colonization is commonly (52.5%) associated with infant colonization. The vertical transmission of GBS from mother to the newborn was corroborated by the high concordance of matching serotypes in the colonized mother-newborn dyads. Our study, however, also identified GBS in 113 (28.1%) of 402 colonized newborns born to mothers in whom GBS was not identified by vaginal swabbing.