Group B Streptococcus


Group B Streptococcus is the most common cause of infection in babies in the first few days of life. The infection may proceed so rapidly that even the most powerful antibiotics do not work and in some babies the infection can prove fatal. In addition, another one in five babies who survive the infection become permanently affected. It is also a recognised but unusual cause of stillbirths and premature onset of labour.

The group B Streptococcus is related to other Streptococci, some of which are better known. The group B Streptococcus bacterium is unusual, however, because it causes infections that most often occur in infants of less than three months of age.


Last updated April 2015 by Professor P Steer, Emeritus Professor of Obstetrics, Imperial College London, UK.

What are the symptoms?

The infection develops most commonly during labour, while the baby is still in the womb or in the first 24 hours after birth. The baby is either unwell at birth or rapidly becomes unwell, will not feed and will have difficulty breathing. This is called ‘early onset disease’ (defined as from birth up to seven days of life) and accounts for over 80% of cases. A less common form of the infection affects babies from seven days after birth up until about three months of age; this is called ‘late-onset disease’ and is not currently preventable by any known strategy. Infections acquired 48 hours or more after birth are often complicated by meningitis as well as septicaemia (blood poisoning).

What are the causes?

In almost all cases of early onset disease, the source of the organism is the mother’s vagina or gastrointestinal tract. Group B Streptococcus is a common organism, which resides in the vagina of millions of women and generally does not lead to any illness. Of all the babies born to mothers who carry the group B Streptococcus, only a small minority will develop infection (as opposed to colonisation, which is where the baby carries the bacterium but it does not cause an infection). There is no way to eradicate group B Streptococcus in the mother by using antibiotics, diet or lifestyle change.

How is it diagnosed?

If infection with group B Streptococcus is suspected, tests will need to be carried out. This may be in the form of a blood test, or a lumbar puncture (where a small amount of fluid from around the baby’s spinal cord is collected).

How is it treated?

Administering penicillin (or another antibiotic if the mother is allergic) to the mother from the onset of labour in high-risk cases will prevent the majority of early onset infections. Those at higher risk can include: those with a raised temperature in labour, a previous episode of group B Streptococcal bladder infection, a history of a previous child that had a group B Streptococcal infection, and women known to be colonised with group B Streptococcus. It is thought by some to be a good idea to give antibiotics to all women in preterm labour, as a precaution. The antibiotic should be given intravenously (into a vein) at the onset of labour and should be continued at four hourly intervals until the baby is delivered.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
Not applicable.

Prenatal diagnosis
A test is available that establishes whether the mother is carrying group B Streptococcus in late pregnancy. Swabs are taken from the anus and lower vagina at 35 to 37 weeks of pregnancy. If the swab shows that the mother is a group B Streptococcus carrier, the risk of group B Streptococcal infection in the baby is increased approximately three fold. Routine screening is not currently advocated in the UK by the UK National Screening Committee or by the Royal College of Obstetricians and Gynaecologists, but testing is available for women with risk factors, or who request it. Both organisations recommend offering antibiotics during labour if the mother is known to be a carrier of group B Streptococcus.

Is there support?

Group B Strep Support

Tel: 01444 416 176

The Organisation is a Registered Charity in England and Wales No. 1112065. It provides information and raises awareness of Group B Streptococcus infection in newborn babies, and offers support to affected families. 

Group details last updated November 2014.

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