Group B Streptococcus (GBS) is a normal bacterium which colonises between 20-30% of adults in the UK, usually without symptoms or side-effects. It is most commonly found in the intestines, as part of the normal gut flora (bacteria living in the gastrointestinal tract). It is also often found in the vagina of adult women. It is known as a ‘commensal’ – an organism which lives on another without causing any harm.

GBS can, however, occasionally cause infection, most commonly in newborn babies. GBS more rarely causes infection in adults (typically women during pregnancy or after birth, the elderly and people with serious underlying medical conditions which impair their immune system) and more rarely still during pregnancy and before labour.

GBS is not a sexually transmitted disease and treatment of a woman and of her partner carrying GBS does not prevent re-colonisation.

Group B Strep Infection in Newborn babies

In newborn babies, there are two types of GBS disease: early and late-onset. Roughly two-thirds of GBS disease is early-onset, occurring in the first 6 days of life and usually apparent at birth. Early-onset GBS disease is normally characterised by the rapid development of breathing problems, associated with blood poisoning. Late-onset disease – which usually presents as GBS meningitis – occurs after the baby is 6 days old and, normally, by age 1 month but, rarely, up to age 3 months. After age 3 months, GBS infection in babies is extremely rare.


GBS is a recognised cause of preterm delivery, maternal infections, stillbirths and late miscarriages.

Preterm babies are known to be at particular risk of GBS infection as their immune systems are not as well developed as those of full-term babies.

Overall, without preventative medicine, GBS infections would affect an estimated 1 in every 1,000 babies born in the UK. Therefore, based on 700,000 babies born annually in the UK, approximately:

  • 230,000 babies would be born to mothers who carry GBS; 88,000 babies (1 in 8) become colonised with GBS; 700 babies would develop GBS infections, usually within 24 hours of birth; and
  • 75 babies (11% of infected babies) would die.

Of the survivors of GBS meningitis, up to one half suffer long-term mental and/or physical problems, from mild to severe learning disabilities, loss of sight, loss of hearing and lung damage (in around 12% of the survivors, the disabilities may be severe). The great majority of survivors of early-onset disease do so with no long-term damage.

*Image taken from Wikimedia Commons