Group B Streptococcus

Group B Streptococcus is a type of bacterium also known as GBS, Group B strep, or Streptococcus agalactiae. GBS infection is the main cause of sepsis and meningitis in babies under 3 months of age in high-income countries, such as the United Kingdom. 50% of babies who develop GBS meningitis will be left with some level of long-term disability such as cerebral palsy, deafness, blindness or learning difficulties. It can also cause stillbirth and may contribute to premature birth. GBS is rare in babies and children over 3 months old, and in adults. See GBS: Trials and Tribulations for more information.

  • Over 319,000 infant cases of GBS infection are thought to occur globally each year, resulting in 57,000 stillbirths and 90,000 infant deaths in 2015.  
  • 1 in 10 babies infected with GBS will die. 
  • In England and Wales there are around 450 cases of GBS infection in babies every year (about 1 in 2000 babies under 3 months old).
  • Overall, 1 in 17,000 babies in the UK die from GBS infection each year.

Learn more in the sections below.


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Like many bacteria, GBS is often present in the body without any symptoms. Up to 3 in every 10 adults carry the bacteria harmlessly in their digestive systems as part of the normal gut ‘flora’. In women, GBS is also commonly found in the vagina. GBS is usually passed from mother to baby around birth, but can also be passed on in other ways.

  • 21.7 million pregnant women carry these bacteria according to the first global study of Group B Strep - most of them are currently unidentified and untreated.
  • A recent study showed that GBS is found in pregnant women in all regions of the world, with almost 1 in 5 pregnant women carrying it.

If a woman is carrying GBS when she gives birth, there is a 1 in 2 chance that the baby will also carry the bacteria on his/her skin. While most babies do not get sick, about 2-3 out of every 100 who have the bacteria living on their skin may develop a serious infection such as pneumonia, meningitis or septicaemia (blood poisoning).

In babies, there are two types of GBS infection: Early-onset (in babies up to a week old) and late-onset (in babies from one week to three months old). Early-onset GBS is caught from the mother during birth and leads to death in approximately 10% of cases worldwide. Late-onset GBS is less understood but could be due to skin-to-skin contact with someone carrying the bacteria. Babies with late-onset GBS often present with Meningitis.

The risk of GBS infection in newborn babies is higher if:

  • the baby is born prematurely (before 37 weeks)
  • the mother has previously had a baby infected with GBS
  • the mother has a high temperature during labour
  • the mother’s waters break more than 18 hours before the baby is born
  • the mother has GBS in her urine during pregnancy (this means she is infected with GBS, as urine is usually sterile)
  • the mother is younger (under 18 years old)
  • there is an infection in the womb during pregnancy (known as chorioamnionitis)
  • there are low levels of antibody to a specific strain of Group B Strep

About 2 out of every 3 cases of GBS are early-onset. Most babies who become infected develop symptoms within 12-24 hours of birth. These include:

  • not feeding well
  • grunting
  • high or low temperature
  • being floppy and unresponsive
  • fast or slow heart rates
  • fast or slow breathing rates
  • irritability

Symptoms are similar for late-onset GBS infection.  


Because of the high risks of GBS, newborn babies with suspected GBS infection are usually given antibiotics immediately. Tests are then done to see if the baby actually has GBS. This involves blood tests and may involve a lumbar puncture (taking a sample of fluid from around the baby’s spinal cord). Antibiotic treatment will stop if the tests are negative and there are no more symptoms of GBS. If the tests are positive, antibiotic treatment will continue for several days (usually 7-10 days).


At least 60 countries have a policy to use antibiotics in pregnancy to prevent GBS of the newborn. 

25 countries including the United Kingdom, the Netherlands and South Africa, have policies based on treating with antibiotics if risk factors are present. These include: 

  • early labour (<37 weeks)
  • waters breaking too early
  • mother having a fever ( >38°C)
  • previous baby with GBS disease
  • GBS detected in the mother’s urine (2)


If a woman is known to be carrying GBS in the vagina she can be given antibiotics through a drip during labour to reduce the risk of early-onset GBS. However, this makes no difference to the number of cases of late-onset GBS. Antibiotics are not given beforelabour starts because GBS tends to come back to the vagina after the course is finished, so there would still be a risk of passing an infection on to the baby. If the GBS is detected in the mother’s urine, then antibiotics are given at the time and again during labour. 

In 35 countries including the USA, Canada and parts of Australia, policies are based on swabbing pregnant women for GBS prior to birth and offering antibiotics. Whilst this can prevent some cases of GBS, there are some drawbacks: 

  • Only a small number of babies will develop GBS infection after birth. It is not possible to tell from screening which babies will get the disease.
  • A test done earlier in pregnancy may not give a reliable indication of whether the mother is a GBS carrier at the time the baby is born.
  • As up to 3 in 10 women carry GBS, routine screening could mean that a very high number of pregnant women would be given high-dose antibiotics that they do not need.
  • The cost of such screening programmes can be high, especially for middle to low income countries.

There are also a number of problems with giving antibiotics to women in labour:

  • There is a risk of severe allergic reactions to the antibiotics
  • Over-use of antibiotics can lead to strains of bacteria that are resistant to antibiotics
  • Research suggests that exposing babies to antibiotics very early in their lives may have other effects.

At present there is no licensed (approved for use) vaccine to prevent GBS.


In 2014, the World Health Organization (WHO) convened the first meeting of the Product Development for Vaccines Advisory Committee. GBS was identified as one of the pathogens with a high burden among neonates and infants that may be amenable to prevention by immunization. In April 2016, a WHO consultation was held on GBS vaccines, concentrating on the development of vaccines for maternal immunisation.

Studies show that a GBS vaccine given to pregnant women may prevent 231,000 baby and mother cases each year.This could potentially prevent most cases of GBS without the need for antibiotics or screening.Babies would still be tested and treated for GBS if they developed symptoms. 

A number of GBS vaccines are being developed throughout the world. A study has shown that mothers’ can pass different strains of GBS antibodies to their baby, depending on what they have been exposed to, and that this can provide protection to their baby after birth. This is important as it helps researchers know that a successful GBS vaccine could pass on protection from mother to baby, and has the potential to prevent this disease in newborns. 

Furthers studies, such as PREPARE to estimate the level of antibodies required for protection against the major GBS types causing disease across European and African sites. This could help to inform what is required of the vaccine.

GBS vaccines have been tested in animals, and in phase I and II trials in adults. These include a recent GBS vaccine that was given to non-pregnant women, with results indicating that the vaccine delayed carriage of the bacteria, with no safety concerns (GBS6). This needs to be assessed in pregnant women to see whether the antibodies would be passed on to provide protection for the baby. Some new vaccines have also been tested in pregnant women, and these have not been found to cause any problems during pregnancy. See for example a study by South African researchers from 2016.

For more information about vaccines in pregnancy, see also Vaccines in Pregnancy.

For information about GBS in pregnancy and newborns, see Patient information leaflet.

More information about Group B Streptococcus can be found on the Group B Strep Support charity website.


Page last updated Friday, January 28, 2022