Streptococcus Group B

The pathogen Streptococcus agalactiae represents group B Streptococcus (GBS). The commonly used term of group B streptococcus or GBS is based on Lancefield grouping that takes into account specific cell wall carbohydrate antigen. It is a common colonizer of the genital and gastrointestinal tracts. GBS colonization in pregnant women is a major risk factor for neonatal and infant infection.

The widespread screening of pregnant women for this organism in the third trimester and subsequent antibiotic prophylaxis for maternal colonization has dramatically reduced the incidence of early-onset neonatal disease from 1.7 cases per 1000 live births in the early 1990s to 0.22 cases per 1000 live births in 2017. Direct medical costs of neonatal disease before prevention were $294 million annually.

This chapter will discuss different aspects of GBS infection in neonates and infants and pregnant women and the elderly.

History: Edmond Nocard first recognized this pathogen in 1887 as a source of bovine mastitis that resulted in agalactia or lack of milk production. Decades later, S. agalactiae gained recognition as a human pathogen responsible for infections, most commonly in pregnant women and newborns. However, the significance of this organism was not discovered until 1938, when Fry described three fatal cases of postpartum sepsis. Numerous reports continued to ascribe neonatal infections to this pathogen until the 1970s, when GBS emerged as the predominant organism causing bacteremia and meningitis in newborns and young infants less than three months old. GBS is also an occasional cause of infections in postpartum women (endometritis) and individuals with impaired immune systems, in whom the organism may cause septicemia or pneumonia.