Group B Streptococcus is a normal bacterium that is present in 10-30% of women’s vagina. It becomes important in childbirth for you if you develop signs of an infection, which can be quite nasty (after you’ve delivered). The infection can be of the womb lining (endometritis) or in the wound if you have had a caesarean section.
Much more importantly for your baby is the disease called Early Neonatal Group B Streptococcal Septicaemia (ENGBSS). This occurs after the baby passes through an infected birth canal and the infection spreads to his blood stream. 30% of affected neonates develop meningitis (an infection of the lining of the brain) and half of these babies will be brain-damaged. 20-30% will die. The baby will carry the bug in 35-50% of labours where a swab taken during labour was positive and in 25% where there was a confirmed swab at some point during the pregnancy. Studies from the US indicate that 1-2% of babies that carry the bug develop ENGBSS, whereas in the UK it is only 0.2-0.5%. In the UK, ENGBSS occurs in 0.3/1000 neonates. In the US it is 3/1000.
There are some well identified risk factors for a baby developing ENGBSS. In addition to a positive swab during pregnancy, the following factors lead to a much increased chance of infection (about 50/1000 as compared to 0.3/1000), and should lead to treatment during labour:
- Prolonged rupture of membranes (>18-24h)
- Preterm labour (<37w)
- Rupture of membranes before 37 weeks
- Temperature during labour
- GBS found in the urine
- Previous infant with ENGBSS
Treatment of GBS-carrier mothers with the above risk factors during labour will lead to a 60% reduction in neonatal infection rate and 95% reduction in neonatal death due to this disease.
In the UK, treatment of mothers with a positive swab, but without these risk factors during labour does not significantly reduce the rate of ENGBSS. The difference in numbers between the US and UK mean that it may be worthwhile screening for this bacteria in the US, whereas in the UK because of its rarity, screening is unlikely to have a significant impact on neonatal deaths.