Prevention of Group B streptococcus infection

Abstract

Group B streptococcus (GBS), also known as Streptococcus agalactiae (S. agalactiae), is a bacterium surrounded by a polysaccharide capsule. Based on the serological reaction against the polysaccharide capsule or as determined by a multiplex polymerase chain reaction assay, GBS strains can be divided into 10 distinct serotypes (Ia, Ib, and II to IX). Multilocus sequence typing is also used to classify GBS strains. More than 750 sequence types (STs) have been identified, and most human isolates are clustered into six major clonal complexes. Some serotypes and/or STs are associated with specific disease phenotypes; for example, some strains are related to neonatal early-onset disease (EOD) and some to late-onset disease (LOD).1Teatero S. Ferrieri P. Martin I. Demczuk W. McGeer A. Fittipaldi N. Serotype distribution, population structure, and antimicrobial resistance of Group B Streptococcus strains recovered from colonized pregnant women.J Clin Microbiol. 2017; 55: 412-422Crossref PubMed Scopus (63) Google Scholar Although GBS may be asymptomatically colonized in the gastrointestinal and genitourinary tracts of healthy human adults, it can sometimes cause serious illness especially in newborns, the elderly, and immunocompromized persons. In mothers, GBS can sometimes cause chorioamnionitis and postpartum infections, and maternal urinary tract infections may induce labor and cause premature delivery and miscarriage. GBS is one of the pathogens causing the highest mortality in neonatal sepsis.2Chen I.L. Chiu N.C. Chi H. Hsu C.H. Chang J.H. Huang D.T. et al.Changing of bloodstream infections in a medical center neonatal intensive care unit.J Microbiol Immunol Infect. 2017; 50: 514-520Crossref PubMed Scopus (26) Google Scholar Colonization of GBS during labor is the primary risk factor for the development of EOD. Vertical transmission of GBS can occur either in utero or during birth through the vagina of a colonized woman. About half of infants born to GBS-colonized mothers are colonized with GBS during birth, and 1–2% of these newborns will develop EOD if proper management is not provided. GBS-LOD is not acquired through vertical transmission during delivery. It is acquired 7 days to 3 months after birth from breast milk or from environmental and community sources. While prevention of GBS-EOD has significantly decreased infection rate, LOD has not benefited much from the prevention. In Taiwan, the maternal colonization rate of GBS was around 20% from January 2004 to June 2005 based on a study in six hospitals, and the incidence of neonatal GBS infection was one per thousand live births.3Yu H.W. Lin H.C. Yang P.H. Hsu C.H. Hsieh W.S. Tsao L.Y. et al.Group B streptococcal infection in Taiwan: maternal colonization and neonatal infection.Pediatr Neonatol. 2011; 52: 190-195Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar The data are similar from 0.7‰ to 3.7‰ live births in the United States and from 0.2‰ to 3.25‰ in Europe before the use of universal GBS antenatal screening and intrapartum antibiotic prophylaxis (IAP) was implemented. After the implantation was initiated in 2012, the GBS prevalence in pregnant women remained near 20%, but the rate of GBS-EOD declined from the original 1‰–0.2‰, a decrease of as high as 80%.4Hung L.C. Kung P.T. Chiu T.H. Su H.P. Ho M. Kao H.F. et al.Risk factors for neonatal early-onset group B streptococcus-related diseases after the implementation of a universal screening program in Taiwan.BMC Public Health. 2018; 18: 438Google Scholar Hsu et al.5Hsu J.F. Chen C.L. Lee C.C. Lien R. Chu S.M. Fu R.H. et al.Characterization of group B Streptococcus colonization in full-term and late-preterm neonates in Taiwan.Pediatr Neonatol. 2019; 60: 311-317Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar enrolled 500 healthy newborns to detect their GBS carriage rate. The GBS colonization rate of healthy neonates' mothers was 23.7%, similar to the previous decade. While the babies of GBS-negative mothers had a GBS carriage rate of 1.6%, the carriage rate was up to 5% for mothers who were screened positive for GBS and even received IAP. The results point out that the threat of GBS infection still exists. The distribution of GBS serotypes in these healthy newborns was somewhat different from patients with invasive diseases.6Lo C.W. Liu H.C. Lee C.C. Lin C.L. Chen C.L. Jeng M.J. et al.Serotype distribution and clinical correlation of Streptococcus agalactiae causing invasive disease in infants and children in Taiwan.J Microbiol Immunol Infect. 2017 Oct 24; (pii: S1684-1182(17)30228-1)https://doi.org/10.1016/j.jmii.2017.09.002Crossref Scopus (19) Google Scholar IAP is currently the only reliable way to prevent GBS-EOD and has been proven to be effective. However, it is considered to be associated with the emergence of resistant bacterial strains and with an increased incidence of EOD caused by other pathogens, including Escherichia coli. Nevertheless, most studies have not found an increased rate of non-GBS early-onset sepsis related to the widespread use of IAP. Because IAP has no effect in preventing either GBS-LOD in infants or GBS infections in adults, GBS vaccination would be a good way to control not only GBS-EOD and GBS-LOD in infants but also infections in adults at risk. Maternal immunization as an adjunctive strategy to IAP in unimmunized pregnant women would prevent more GBS cases. Transplacental maternal-specific antibodies may be able to provide protection to babies against GBS infection. The capsular polysaccharide of GBS, as an important virulence factor, is also an excellent candidate for the development of an effective vaccine. Choosing the most suitable serotypes for vaccine production is of great importance. At present, there is no licensed GBS vaccine in the market. Despite the promising results from clinical trials, the phenomenon of serotype switching and replacement has been noted worldwide.7Lin S.M. Zhi Y. Ahn K.B. Lim S. Seo H.S. Status of group B streptococcal vaccine development.Clin Exp Vaccine Res. 2018; 7: 76-81Crossref PubMed Scopus (44) Google Scholar Ongoing surveillance to monitor GBS serotype distribution will be necessary to guide the development and use of GBS conjugate vaccines. None.