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What is Strep B?

This common infection is carried by up to a third of all men and women, but how can it affect your baby if you have it during pregnancy?

Posted: 30 October 2007
by Louise Rogers

What is Strep B?
Strep B, or group B streptococcus (GBS) is an infection carried by up to a third of all men and women in their intestines without symptoms; roughly a quarter of women of childbearing age carry GBS in the vagina at any one time. GBS is a normal body commensal (an organism that lives on another without harming it); colonisation is normal and does not require treatment with antibiotics.

So what’s the problem?
Since the 1970s, GBS has been recognised as the most common cause of bacterial infection in newborn babies, usually presenting within the first 24-48 hours after birth, resulting in disease at birth and up to three months of age.
A pregnant woman who carries GBS can pass it onto their baby around birth.

What will it do to my baby?
In newborn babies, there are two types of GBS disease: early and late-onset. Roughly 80% of GBS disease is early-onset, occurring in the first two 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 two days old and, normally, by age one month but, rarely, up to three months. After three months, GBS infection in babies is extremely rare. In the most extreme cases, babies can die.
Of the survivors of GBS meningitis, up to a third suffer long-term mental and/or physical handicaps, from mild learning disabilities to severe mental retardation, 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.

What’s my risk factor?
Overall, without preventative medicine, GBS infections affect an estimated one in every 1,000 babies born in the UK (about 700,000 babies are born annually in the UK). In other words, 230,000 babies are born to mothers who carry GBS; 88,000 babies (one in eight) become colonised with GBS; of these, 700 babies develop GBS infections, usually within two days of birth; and 75 babies (11% of infected babies) die.

Can it be prevented?
Yes. You can be tested for GBS, although this is not routinely offered on the NHS, and the type of test used by the NHS is regarded as unreliable. The test is available privately, and costs about £32. It is sent in the post so can be done by anyone, anywhere in the UK.
Two swabs need to be taken, one lower vaginal, one rectal. As GBS can naturally come and go from the vagina the test should be done at 35-37 weeks of pregnancy. Working on a five-week window the results will tell you whether GBS is likely to be present at birth.
A positive swab result for GBS means a woman is colonised with GBS at the time the swab was taken – not that she or her baby will become ill.

What happens if I test positive?
In this case, you will be offered IV antibiotics every four hours during labour; this significantly reduces the chances of infection to the baby. For a normal, pregnant woman carrying GBS at delivery with no other risk factors, the chances of her baby developing a GBS infection where no preventative medicine being given is around one in 300; if she has the IV antibiotics the risk drops to smaller than one in 6000.

What other risk factors?
About 60% of babies who develop GBS infection have added risk factors, each of which increases the chance that he or she will contract GBS.

  • Where labour or membrane rupture is preterm, ie, before 37 weeks of pregnancy

  • Where there is prolonged rupture of membranes (more than 18-24 hours before delivery)

  • Where the pregnant woman has a raised temperature (37.8°C or higher) during labour.

If you choose not to have the IV antibiotics during labour, it is useful to bear these risk factors in mind, so you can choose to have the antibiotics should any of these situations arise.

Where can I find out more?
The UK support group, which is campaigning for the test to be routinely offered on the NHS, has a website offering excellent information and advice. Group B Strep Support:, 0870 803 0023.

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