The route of vertical transmission of Group B streptococcus (GBS) from maternal colonisation resulting in neonatal GBS early-onset disease (GBS EOD) is well known, whereas the aetiologies of neonatal transmission in GBS late-onset disease (GBS LOD) remain less clear. Maternal GBS colonisation is one of the potential risk factors for GBS late-onset disease. Yet, the steady rates of GBS LOD despite the extensive use of intrapartum antibiotic prophylaxis for women colonised with GBS suggest the role of a postpartum colonisation from a horizontal maternal transmission, healthcare or community source.

In this issue of the journal, Chan and colleagues describe nearly a decade of neonatal and infant sepsis outcomes after the enactment of universal screening for maternal GBS colonisation with implementation of intrapartum antibiotic prophylaxis for a positive GBS screen (Chan et al. BJOG 2022; https://doi.org/10.1111/1471-0528.17279). Their findings corroborate a growing body of evidence that in populations with increased rates of neonatal GBS EOD, screening-based protocols for maternal GBS colonisation with intrapartum antibiotic prophylaxis are associated with lower incidences of GBS EOD disease compared with risk-based strategies (Hasperhoven et al. BJOG 2020;127:680–91]. Yet the unique observation in this large cohort of more than 467 000 births, there was not only a 75% decrease in the rate of GBS EOD but a 44% decline in the incidence of GBS LOD as well. Other studies around the world making use of similar screening and treatment interventions have not noted decreases in the rates of GBS late-onset disease (Nanduri et al. JAMA Pediatr 2019;173:224–33]. So one must ask, what might cause this reduction in the incidence of GBS late-onset disease? Are there unique characteristics of this populace that could account for this?

During the 3-year risk-based screening period the ratio of GBS EOD to LOD of 1.47 fell within the range of what is reported worldwide (1.72, 95% confidence interval [CI] 1.35–2.21), suggesting a similar disease burden (Madrid et al. Clin Infect Dis 2017;65(Suppl 2):S160-72]. Risk factors for GBS LOD have included preterm birth, young maternal age and positive maternal GBS screen. Although the current study could not provide details of the individual cases of infant sepsis or the rate of adequate GBS screening and administration of intrapartum antibiotic prophylaxis, past analysis of risk factors for LOD GBS have not shown them to be affected by the implementation of universal GBS screening and intrapartum antibiotic administration (Pintye et al. J Pediat Infect Dis Soc 2016;5:431–8). One must interpret cautiously studies with consecutive intervention groups, as a risk of performance bias may exist, with the observed effect inherent in systematic differences between groups in healthcare provided or exposure to factors other than the interventions of interest. Despite the encouraging reduction in GBS LOD noted in the current trial, GBS LOD continues to be a major cause of perinatal morbidity and mortality even with the implementation of universal GBS screening.

B 族链球菌 (GBS) 的母体定植导致新生儿 GBS 早发性疾病 (GBS EOD) 的垂直传播途径是众所周知的，而 GBS 晚发性疾病 (GBS LOD) 中新生儿传播的病因尚不清楚. 母体 GBS 定植是 GBS 迟发性疾病的潜在危险因素之一。然而，尽管对 GBS 定植的妇女广泛使用产时抗生素预防，但 GBS LOD 的稳定比率表明产后定植的作用来自横向母体传播、医疗保健或社区来源。

在本期杂志中，Chan 及其同事描述了在对母体 GBS 定植进行普遍筛查以及对 GBS 筛查阳性实施产时抗生素预防后近十年的新生儿和婴儿败血症结果（Chan 等人BJOG 2022；https //doi.org/10.1111/1471-0528.17279）。他们的研究结果证实了越来越多的证据表明，在新生儿 GBS EOD 发生率增加的人群中，与基于风险的策略相比，基于筛查的母体 GBS 定植方案和产时抗生素预防与较低的 GBS EOD 发病率相关（Hasperhoven 等人.比约格2020；127：680–91]。然而，在这个超过 467 000 名新生儿的大型队列中的独特观察发现，不仅 GBS EOD 发生率下降了 75%，GBS LOD 发生率也下降了 44%。世界各地使用类似筛查和治疗干预措施的其他研究并未注意到 GBS 迟发性疾病的发病率下降（Nanduri 等人，JAMA Pediatr 2019；173：224-33）。因此，必须问，什么可能导致这种 GBS 迟发性疾病发病率的降低？这个人群是否有独特的特征可以解释这一点？

在基于风险的 3 年筛查期间，GBS EOD 与 LOD 的比率为 1.47，处于全球报道的范围内（1.72，95% 置信区间 [CI] 1.35–2.21），表明相似的疾病负担（马德里et al. Clin Infect Dis 2017;65(Suppl 2):S160-72]。GBS LOD 的风险因素包括早产、年轻产妇年龄和产妇 GBS 筛查阳性。尽管目前的研究无法提供个案的详细信息婴儿脓毒症或适当 GBS 筛查率和产时抗生素预防给药的比率，过去对 LOD GBS 危险因素的分析未显示它们受到实施普遍 GBS 筛查和产时抗生素给药的影响（Pintye 等人，J Pediat感染Dis Soc2016 年；5:431–8）。人们必须谨慎地解释连续干预组的研究，因为可能存在性能偏差的风险，观察到的效果是在所提供的医疗保健或暴露于感兴趣的干预措施以外的因素的组之间的系统差异中固有的。尽管在当前试验中注意到 GBS LOD 的减少令人鼓舞，但即使实施了普遍的 GBS 筛查，GBS LOD 仍然是围产期发病率和死亡率的主要原因。