Group B Streptococcus is a major cause of invasive infections in neonates, with the colonization of the vaginal-rectal tract of pregnant women being the main transmission source. Our data provide updated insights about the prevalence of vaginal-rectal GBS colonization in pregnancy. In addition, the present study shows the rates of adhesion to GBS screening and to IAP in a cohort of pregnant women referring to a II level University Hospital in the city of Palermo, Italy. In our sample, the prevalence of subjects screened for GBS out of the total addressed to our Mother and Child Department was 73.92%; complete vaginal–rectal screening for GBS was conducted in all cases. Such data were higher than those of a previous retrospective study carried out in our Hospital in 2012, and also than the rates recorded by Berardi A. et al. in 2011 in Central Italy, which were 66.03% and 67.9% respectively (Fig. 8a) [19, 20]. According with CDC and the Italian Obstetrics Society guidelines, the execution of vaginal–rectal cultures for GBS is recommended between 35 and 37 weeks of gestation, and such indications were those followed also in the present study [8, 13]. In our population vaginal and rectal swabs were positive for GBS in the 10.42% of cases; this value is at the lower range of the national average, which is between 10 and 20% [21]. Comparing the current analysis with that carried out in 2012 in our Hospital, an increased prevalence of GBS colonization in our population has been observed in the last few years (from 7.98–11.42%) (Fig. 8b) [19].
Figure 8a/b. Comparison of GBS screening among the current study and those previously reported in our Hospital and in Central Italy (a), and of maternal GBS colonization between present analysis and that conducted by Puccio et al. in 2012 in our Department (b)
Worldwide, frequencies of maternal GBS carriers have been reported to range from 14 to 30% in high-income countries (mildly higher than the present survey), to be around 19% in the Sub-Saharan region, and 12–15% in India and Pakistan (Fig. 9) [22–24]. Differences in the detected rate of vaginal-rectal GBS colonization may reflect the different demographic characteristics of the populations under investigation. Actually, GBS incidence rates can vary, either according to geographical region or time period [25]. Indeed, when comparing COVID-19 with the post-pandemic scenario, we detected a mild decrease in GBS maternal colonization during the years 2020–2021 (11.38% vs 11.5%).
Figure 9. Comparison of maternal GBS colonization rates among current study and those reported in other regions worldwide
Amongst our overall sample, only 21.48% women received adequate IAP in presence of clinical indications (positive GBS screening culture or intrapartum risk factors). The consequent higher rate of subjects who did not receive or performed incomplete/inadequate IAP can be due to those women admitted in advanced labor or presenting with a precipitous one, in addition to the few cases in which it was omitted for misinterpreted/incorrect data on GBS status at delivery. In Central Italy a major proportion (> 90%) of individuals showing GBS-positive cultures received adequate treatment [20]. In the USA, the prevalence of mothers with an indication for IAP who received adequate treatment increased, from 73.8% between 1998 and 1999 to 85.1% between 2003 and 2004 [26, 27]. Comparing the pandemic period (years 2020–2021) with the following one (2022), a lower frequency in the execution of vaginal-rectal swabs for GBS, as well as of adequate and complete IAP, were found in the first two years than in 2022 (Fig. 5a/b). In fact, during the COVID-19 period, isolation, mask wearing, hand hygiene, and other infection control and preventive measures adopted to lessen the pandemic's effects resulted in a decrease in the access to various health facilities, including obstetric and perinatal care services. This reduction was attributed to the concern of getting sick perceived by people, as well as to the challenges in maintaining the support of other family members during the hospital stay [11, 12]. Finally, we detected inequalities between the Italian women and the foreign ones due to the major number of swabs performed among the former and, although not statistically significant, higher colonization rates in the latter.
Moreover, we reported an EOD prevalence of 7.69% among children of mothers carrying risk factors, and of 6.06‰ on the total number of newborns delivered during the 3-year investigation. In our study the clinical picture of the early form of disease was represented by sepsis. According to literature, respiratory signs were the initial most common typical symptoms, only preceded by poor feeding/regurgitation associated with hypotonia, frequently described in literature reports as well [28]. The other less common clinical manifestations identified were fever, jaundice, and septic shock, which are not typical of GBS, and which can occur in other bacterial infections. Mortality is estimated to be 2–5% in full-term children, and increases by 25% in preterm infants; nonetheless, in our sample (in which, however, no preterm babies were present) neither deaths nor meningitis were documented [29, 30]. It is noteworthy that, as expected, none of the mothers’ patients received adequate IAP.
This study further highlights how relevant could be to begin IAP as soon as possible, when a clinical indication is identified (positive GBS screening culture, previous child with GBS disease, bacteriuria documenting GBS in the current pregnancy, in addition to those women whose GBS status is unknown at labor onset and at least one of the risk factors pointed out by CDC) [8]. This is due to the beneficial effects of IAP, which are fully reached when it is started at least four hours before birth. Our results demonstrate that there is still a relevant number of women colonized with GBS at delivery who did not perform appropriate IAP, or even who is not recognized as GBS-positive by antenatal screening cultures. The current research underlines how crucial could be the definition of pregnant women's GBS colonization status, through vaginal and rectal swabs obtained between 35 and 37 weeks of gestation. Indeed, the identification and treatment of candidates for IAP are necessary, as moreover evidenced by the present study, also owing to the higher risk of developing EOD for neonates born to mothers without GBS screening and not receiving adequate and/or complete IAP.
In order to stop and/or limit GBS infections, local public health organizations should support both microbiological surveillance and educational initiatives [31, 32]. These interventions, actually, are able to reduce by 80% the risk of neonatal sepsis or meningitis, specifically early onset ones, i.e. those between birth and the completion of the 6th day of life [33]. Indeed, such strategies cannot be effective in the remaining 20% of early infections, as they are not linked to fetal contamination with the bacteria encountered during the passage through the vaginal canal at birth. They are, rather, dependent on infections contracted prior to the delivery, due to the ascending passage of germs to the fetus, especially in case of premature rupture of membranes. Furthermore, IAP is not active for late infections, i.e. those occurring between the 6th and the 89th day of life. In these cases, in fact, baby's infection relies on extrapartum factors, generally contamination of the mother while caring for the child, intra-hospital spread by other colonized patients or through breast milk [34, 35]. Although the total number of cases of neonatal GBS infection is not reported to be overly high, as highlighted also in the present analysis, however it is clear that the prophylaxis measures adopted to date cannot be considered fully satisfactory. Pregnant woman screening, indeed, is not always easy to implement, as well as the administration of intrapartum antibiotics, which often does not follow in the clinical daily practice (as evidenced in our experience), the effective modalities established by CDC guidelines for the eradication of the bacterium. Clinicians, then, need to be careful and accurate in the correct adhesion to care protocols, also in consideration of the significant number of incomplete cultures performed and incorrect IAP administrations, as documented by the present analysis. In addition to the implementation and improvement of antibiotic prophylaxis, however, the search for alternative preventive tools, such as the production of an effective and safe vaccine administered to the mother, appears urgent and not postponable [36–38]. Nonetheless, its production has set many difficulties in the realization process. They are linked to the presence of at least 10 GBS strains showing a different capsular polysaccharide, which is the major virulence factor of the bacterium. Specifically, 6 of them (Ia, Ib, and II up to V) are the most frequently involved in invasive disease [37]. Finally, it is necessary both to establish the best administration time during pregnancy, and any potential harmful effects to the embryo and/or fetus [39]. The results of research are ongoing, pointing at promising perspectives in obtaining a vaccination able to prevent invasive GBS disease in the majority of cases [39].