Hopes for vaccination for Group B Streptococcus

A vaccine for Group B Streptococcus (GBS), the most common cause of severe infection in babies under three months of age, may be available within the next decade. However, in the meantime, the introduction of a screening test during labour could help reduce its potential damage.

There are two types of GBS disease – which can cause meningitis, pneumonia and sepsis in babies. “Early onset” occurs within seven days of birth and is acquired during labour or birth; “Late onset” is between seven and 90 days after birth.

Both may cause significant illness, disability, and can even prove fatal in about 5 per cent of cases.

GBS can also result in miscarriage, stillbirth and preterm delivery. According to obstetrician Keelin O'Donoghue from Cork University Maternity Hospital, 1-2 stillbirths in Ireland each year are reported as due to GBS, "GBS is an important component of the worldwide burden of 2.6 million stillbirths, accounting for around 1 per cent of stillbirths in developed countries and 4 per cent in sub-Saharan Africa. "

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Invasive GBS disease in infants became a notifiable disease here in 2012. Last year, there were 65 cases. Two of these presented with meningitis and two were associated with stillbirth. A total of 394 GBS disease cases were notified to the Health Protection Surveillance Centre between January 2012 and August 2017. The majority, 262, were “Early onset”.

Obstetrician Dr Maeve Eogan from the Rotunda Hospital in Dublin explains about "Early onset" GBS: "A huge number of us (almost one in five in a recent Rotunda study) carry GBS in our system. It is what we call a commensal, it doesn't make us sick as it is part of our normal flora. However, the problem is when somebody carries GBS at the time they give birth, there is a small possibility that their baby can become sick. That's why parents may be very anxious to be screened for it."

The administration of antibiotics to women during labour can help prevent “Early onset” GBS disease. “However, the problem is how you identify the women who should have antibiotics in labour,” says Eogan. “You could say, why not give antibiotics to everybody in labour, but obviously that’s associated with over-medicalisation of labour and birth, as well as adverse effects including allergy, anaphylaxis, and antibiotic resistance.”

So what about screening, which involves testing vaginal swabs during pregnancy?

There isn’t a simple solution here either. Routine universal screening of all pregnant women between 35-37 weeks of pregnancy is currently recommended in the US and many European countries. If a woman tests positive they will be treated with antibiotics in labour. Ireland currently has no formal national guidelines on screening for GBS .

However, our maternity services follow UK guidelines which advocate a "risk-based" approach. This means that antibiotics are offered to women in labour who meet certain "risk" criteria. These include having a previous baby affected by GBS, a urine infection which has tested positive for GBS during pregnancy, waters being broken for more than 18 hours, or a high temperature during labour. Other countries including the Netherlands and New Zealand also follow this "risk-based" approach.

“So you either screen everybody, or you treat people according to risk factors,” says Eogan. “The problem with screening everybody in pregnancy is that carriage of GBS can be transient, so I could have a swab at 35 weeks in my pregnancy and it could identify that I have GBS, and I would receive antibiotics in labour although the GBS might have already cleared from my system.

The converse of that is that I might screen negative at 35 weeks and everybody is totally reassured during the course of my labour, but I actually have acquired GBS between 35 weeks and the time I went into labour.”

A public campaign is under way in the UK seeking the introduction of routine universal screening. However, the most recent guidelines from the Royal College of Obstetricians and Gynaecologists in September recommend continuing the “risk-based” approach.

It's a rapid, user-friendly test that, most of the time, gives a definitive yes or no result

Eogan believes an interim solution until vaccination is available – at least for “Early onset” GBS – is testing in early labour, or just before labour begins. She and colleagues at the Rotunda Hospital have already trialled PCR (Polymerase Chain Reaction) testing successfully in a pilot study and see its potential benefits.

“The optimum time to test, if you had all the resources at your disposal, would be when somebody is in early labour or about to go into labour,”she says. “It’s a rapid, user-friendly test that, most of the time, gives a definitive yes or no result. It’s not the total answer to GBS, that’s where vaccination comes in, but, it pinpoints women who are actually carrying GBS in labour, and means only women who test positive are given antibiotics.”

At the National Maternity Hospital, as part of their efforts to reduce antibiotic consumption, rapid testing is also currently being trialled for women whose waters have broken for a prolonged period but are not in labour, and have no evidence of infection. Only if they test positive are antibiotics administered. The protocol for a positive GBS result also includes immediate induction of labour to reduce exposure for the baby.

The introduction of routine PCR testing nationally would have cost and resource implications, including new machinery, and either additional laboratory staff, or training of already busy staff on labour and emergency ward. However, it would identify babies who are at risk from GBS and require both antibiotics in labour, and additional testing and care when born.

Only Early Onset GBS disease, however, is protected against by antibiotics in labour. A vaccine could protect against both types, and play a role in reducing stillbirths. It would also reduce antibiotic exposure for mothers and babies.

“There has been a lot of work internationally on a GBS vaccine, and there is hope that vaccination will provide a solution for both early and late onset, and all sub-types of GBS,” says Eogan. “Several vaccines are in various stages of development and clinical trials and there are high hopes that this will be the solution in the next 5-10 years. It would be very positive if screening at the onset of labour could be offered in the interim, until vaccination is available.”