Group B Strep

Group B Streptococcus (also known as ‘group B Strep’ or ‘GBS’) is a natural bacterium that is commonly found in the intestines of up to one in every three adults as well as in the vaginas of one in four women. GBS carriage is not an infection; it is some of the natural bacteria that live on and in us. It is defined as a ‘commensal’, an organism that lives on another without causing harm.

Group B Strep Facts

Why do we worry about GBS?

Even though group B Strep is a natural and normal bacterium, it can occasionally cause infection, most commonly in newborn babies. Newborn babies do not have well developed immune systems because they have not had the chance to build them up and are susceptible to some bacteria. Overall, the risk of your baby getting GBS infection without preventative medicine is:

1 in 1,000* where the woman’s GBS carriage status is not known;
1 in 400 where the woman is carrying GBS during the pregnancy;
1 in 300 where the woman is carrying GBS at delivery; and
1 in 100 where the woman has had a previous baby infected with GBS.
*This is a broadly accepted estimate of the number of GBS infections in newborn babies that would occur if no preventative intravenous antibiotics in labour are given and has been used throughout this document. UK research suggested this may be a serious underestimate of the incidence of GBS infection in newborns, which could be as high as 3.6 per 1,000 (Reference: Estimated early-onset group B streptococcal neonatal disease. Luck S, Torny M, d’Agapeyeff K, Pitt A, Heath P, Breathnach A, Russell AB. Lancet, June 2003).


Currently, the UK rate of group B Strep infections in newborn babies in the era of the Royal College of Obstetricians & Gynaecologists’ risk-based prevention strategy is approximately 1/2000, which is 0.05% of all births. Whilst the large majority of babies born to mums carrying group B Strep at the time of delivery are absolutely fine, if a baby does develop a GBS infection, it can be very serious.

When can GBS effect babies?

There are two types of GBS infection:

Early-onset GBS infection. This occurs in the first 6 days of life and usually present as septicaemia with pneumonia. The signs/symptoms can include poor feeding, irritability, grunting, high temperature, fast (or slow) breathing, blueness of the skin, and/or lethargy. Early-onset GBS accounts for up to three out of every 4 (75%) GBS infections in babies.
Late-onset GBS infection. This occurs from 7 days to 3 months of age and accounts for approximately one in every four GBS infections in babies. As your baby gets older, the chance of GBS infection reduces and GBS infection after age 3 months is rare. Late-onset GBS infections tend to present as septicaemia, pneumonia and/or meningitis with symptoms like high pitched cry/moaning, floppy, turns away from bright light, trance like stare, pale/blotchy skin, irritability, dislike of being handled, involuntary stiff or jerking movements and/or tensing of the soft spot on the baby’s head.

The list of symptoms is not exhaustive and babies usually present with some of these symptoms (not all).

If you are in any doubt, it is best to seek medical advice from your GP or A&E department as soon as possible.

How ill I know if I have GBS?

In the UK, women are not routinely tested for group B Strep, instead a risk based approach to prevention is used. The standard NHS test is can be unreliable when it gives a negative result – only half of the women carrying GBS when the samples are taken using the ‘standard’ NHS test – other bacteria present on the swab may outgrow and ‘swamp’ the GBS. A positive result from this method is highly reliable though as there are very few false positives. There is a highly sensitive test specifically for detecting group B Strep carriage called the Enriched Culture Method (ECM) test. It is described by Public Health England but it is not widely available in the NHS. The NHS trusts which offer this test are listed on the Group B Strep Support website, together with organisations that offer this test privately.

While group B Strep carriage does not itself cause any vaginal symptoms, it can sometimes be detected when you have had a vaginal swab taken during your pregnancy.

If you have a urinary tract infection caused by group B Strep, it will usually be grown from the urine specimen when it is sent for culture.

You may be offered a vaginal swab in some circumstances:

Your waters may have broken and you are not in labour
You are in early labour
You are in premature labour
You have increased vaginal discharge
You have vaginal bleeding

Will I automatically be treated?

If your vaginal or rectal swab shows GBS carriage, you will not be treated until you are in labour or your waters have broken. If GBS was found in your urine, you are usually prescribed a course of oral antibiotics and then also offered intravenous antibiotics in labour.

The Royal College of Obstetricians & Gynaecologists (RCOG) recommends that intravenous antibiotics should be offered from the start of labour and at intervals until delivery when:

Mum has previously had a baby with GBS infection.
GBS has been detected in the urine or from a swab during the current pregnancy.
Mum has a fever (>38°C) in labour
Mum has signs of chorioamnionitis

Some hospitals will offer intravenous antibiotics in labour to Mum who are in preterm labour (before 37 completed weeks of pregnancy) and either her waters break before labour or go more than 18 hours before the birth.

The antibiotic recommended to be given intravenously in labour is Penicillin G and doses are repeated every 4 hours. If you are allergic to Penicillin, you must tell your health professionals and Clindamycin is the usual alternative (repeated every 8 hours).

Will my baby automatically be treated?

If a newborn baby develops GBS infection, then 9 out of 10 will show signs of illness in the first 12 hours after birth.

For babies born in higher-risk situations:

If you have had intravenous antibiotics for MORE than 2 hours before delivery, your baby should be:

carefully assessed by an appropriately trained Paediatrician or Advanced Neonatal Nurse Practitioner
If completely healthy, no antibiotics for the baby are required
A period of monitoring (12-24 hours) may be appropriate for those at highest risk of infection.

If you have had intravenous antibiotics for LESS than 2 hours before delivery, your baby should be either:

Examined thoroughly and investigated by a Paediatrician as appropriate.
Observed for a minimum of 12 hours, ideally 24 hours.
If completely healthy, no antibiotics for the baby are required.

For well babies at highest risk of infection, monitoring (12-24 hours) may be appropriate and this should be undertaken as a minimum if the baby is not screened and treated for infection.

If there is any doubt about whether an infection is present, the baby should be started on intravenous antibiotics until it is known that s/he is not infected.

More information

Group B Strep Support | | 01444 416176


Prevention of early onset neonatal Group B Streptococcal disease. RCOG green top guideline no.36. July 2012 (RCOG guideline)