Maternal colonization with Streptococcus agalactiae and associated stillbirth and neonatal disease in coastal Kenya

Abstract

Streptococcus agalactiae (group B streptococcus, GBS) causes neonatal disease and stillbirth, but its burden in sub-Saharan Africa is uncertain. We assessed maternal recto-vaginal GBS colonization (7,967 women), stillbirth and neonatal disease. Whole-genome sequencing was used to determine serotypes, sequence types and phylogeny. We found low maternal GBS colonization prevalence (934/7,967, 12%), but comparatively high incidence of GBS-associated stillbirth and early onset neonatal disease (EOD) in hospital (0.91 (0.25-2.3)/1,000 births and 0.76 (0.25-1.77)/1,000 live births, respectively). However, using a population denominator, EOD incidence was considerably reduced (0.13 (0.07-0.21)/1,000 live births). Treated cases of EOD had very high case fatality (17/36, 47%), especially within 24 h of birth, making under-ascertainment of community-born cases highly likely, both here and in similar facility-based studies. Maternal GBS colonization was less common in women with low socio-economic status, HIV infection and undernutrition, but when GBS-colonized, they were more probably colonized by the most virulent clone, CC17. CC17 accounted for 267/915 (29%) of maternal colonizing (265/267 (99%) serotype III; 2/267 (0.7%) serotype IV) and 51/73 (70%) of neonatal disease cases (all serotype III). Trivalent (Ia/II/III) and pentavalent (Ia/Ib/II/III/V) vaccines would cover 71/73 (97%) and 72/73 (99%) of disease-causing serotypes, respectively. Serotype IV should be considered for inclusion, with evidence of capsular switching in CC17 strains.

Figure 1. Sudy design and recruitment of participants by study site

a, Recruitment timeline and sub-studies undertaken at each study site. b, Recruitment of mothers in the cohort study. *The denominator for live-births in the prospective cohort period, used to calculate incidence of early onset disease in Kilifi County Hospital (KCH) excluded those who did not deliver, or had a stillbirth (leaving 6598.**These mothers (7967) were included in the analysis of risk factors for maternal GBS colonisation. §These births (7833) were included in analyses assessing GBS as a risk factor for stillbirth or perinatal death. §§These live-births (7408) were included in analyses assessing GBS as a risk factor for preterm birth, low birth-weight or possible serious bacterial infection. c Recruitment for the vertical transmission study (maternal-neonatal dyads), a subset of mothers who delivered in KCH. d Recruitment for stillbirth nested case-control study including mothers who delivered in KCH and had a stillbirth, and controls.

Figure 2. Interaction of risk factors at delivery with maternal GBS colonisation associated with adverse newborn outcomes.

Interactions between maternal risk factors at delivery (maternal fever, maternal urinary tract infection, prolonged rupture of membranes) and adverse perinatal outcomes (very preterm birth, very low birth weight, stillbirth, possible serious bacterial infection), in the presence and absence of maternal GBS colonisation. Odds ratios are given for maternal exposures and associated perinatal outcome (listed vertically) with 95% confidence intervals illustrated with error bars for the odds ratio in each case. Interactions were included in multivariable models if there was evidence of interaction at the p<0.1 level in univariable analyses. P values given here are for interaction tests in imputed multivariable models (details for all models in Supplementary tables 5-9). **Possible serious bacterial infection (pSBI) is defined in Supplementary Table 1; it is a clinical diagnosis used to guide empiric treatment of neonates for possible serious bacterial infections in resource-poor settings.

Figure 3. GBS types colonising mothers and causing disease.

a, Invasive neonatal GBS disease cases decrease after the first few days of birth in Kilifi County Hospital neonatal admissions (1998-2013), and serotype III causes an increasing proportion of disease; b: The clinical infection syndrome is predominantly sepsis in the first few days after birth in neonates admitted with invasive GBS disease to Kilifi County Hospital (1998-2013) with increasing numbers of neonates admitted with meningitis with or without sepsis later in the neonatal period; c, The percentage of different serotypes in GBS isolates from maternal colonisation, early onset disease (EOD) and late onset disease (LOD) in neonates shows a stepwise increase in serotype III from maternal colonisation to EOD and LOD; d, The percentage of different clonal complexes in GBS isolates from maternal colonisation, neonatal sepsis and neonatal meningitis (+/- sepsis) shows the increasing dominance of CC-17 in neonatal disease, particularly in neonatal meningitis.

Figure 4. Phylogenetic reconstructions of GBS isolates

Maximum likelihood phylogenies, with recombinant regions removed, are shown separately for each clonal complex. Background shading indicates ST-17 isolates within CC-17. Serotypes are illustrated for each clonal complex in the innermost circle. The next circle describes the sample source of the GBS isolate (neonatal invasive, or maternal colonising (by site of recruitment)). For maternal colonising isolates, epidemiological details are illustrated. From the outermost circle, these are: maternal HIV status (negative, HIV-infected, HIV infected and taking prophylactic co-trimoxazole), socio-economic status (high, medium, low and very low), ethnicity (Mijikenda or non-Mijikenda) and the presence or absence of cattle contact.