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Group B streptococcal infections - Frequently Asked Questions

What are group B streptococci and how are they classified?

Lancefield group B streptococci (GBS), also called Streptococcus agalactiae, form part of the normal bacterial flora of the female genital tract and can be part of normal skin and gut bacteria of men or women. Under certain conditions, GBS can act as an opportunistic pathogen, causing serious disease. The term group B refers to the presence of a particular antigen on the surface of the bacterium, which is used for laboratory identification. Streptococci are grouped according to these surface antigens, each type of antigen being allocated a letter of the alphabet; hence we have Lancefield groups A to W (excluding I and J), named after Dr Rebecca Lancefield who first devised this classification scheme. Streptococci are also classified into pyogenic ('pus-forming') streptococci, which include groups A, B, C, and G, and non-pyogenic (non "pus-forming') streptococci which encompasses the mitis, anginosus, bovis, salivarius and mutans sub-groups. Streptococcus pneumoniae, otherwise known as pneumococcus, forms its own distinct group.

Which diseases are caused by group B streptococci?

GBS are mainly associated with disease in newborns ('neonates'), such as meningitis, septicaemia and pneumonia, but can also cause septic abortion (loss of a pregnancy as a result of a bacterial infection) and puerperal sepsis (destruction of maternal tissues at or following childbirth as a result of bacterial infection). They can also cause non pregnancy-related disease among adults, for example urine or blood stream infections.

How common are these infections in the UK?

A 2001 UK study of severe GBS disease in infants See CDR Weekly Volume 12 no. 16

The incidence of invasive GBS disease in adults is considerably lower, a rate of 8.4 and 5.8 per 100,000 population for males and females aged 75 and over been reported for 2004 in England, Wales and Northern Ireland. See CDR Weekly Volume 15 no. 24.

How are group B streptococcal infections spread?

Neonatal infection may be divided into two types:

  • Early Onset Disease (EOD), which occurs in the first week of life. In these cases the source of the infection is usually the mother's genital flora.
  • Late Onset Disease (LOD), which occurs between the 7th and 90th day of life. In these cases the infant is presumed to have been infected after the birth, and as such may have acquired their infection whilst in hospital e.g. cross-infection in neonatal units.

GBS infection in older adults is often associated with urinary tract infection (cystitis), or infections of pre-existing wounds or lesions eg diabetic foot ulcers.

 

What treatments are available for group B streptococcal infections?

Antibiotic treatment, usually, with penicillin, erythromycin or ampicillin can be used to both treat and help prevent GBS infection.


Last reviewed: 18 December 2008