Modelling the effect of the introduction of antenatal screening for group BStreptococcus(GBS) carriage in the UK

Abstract

ObjectivesTo estimate the potential impact of the addition of culture-based screening for group B streptococcus (GBS) carriage in pregnancy to a risk-based prevention policy in the UK. We aimed to establish agreement within a multidisciplinary group of key stakeholders on the model input parameters.DesignDeterministic model using a consensus approach for the selection of input parameters.Setting and participantsA theoretical annual cohort of 711 999 live births in the UK (excluding births by elective caesarean section).InterventionsCulture-based screening for GBS at 35–37 weeks of pregnancy added to the recommended risk-based prevention policy in place on the date of modelling.Outcome measuresOutcomes assessed included use of intrapartum antibiotic prophylaxis (IAP), early onset GBS (EOGBS), EOGBS mortality, severe EOGBS-related morbidity and maternal penicillin anaphylaxis.ResultsWith no prophylaxis strategy, the model estimated that there would be 421 cases of culture positive EOGBS in a year (0.59/1000 live births). In the risk-based prophylaxis scenario, 30 666 women were estimated to receive IAP and 70 cases of EOGBS were prevented. Addition of screening resulted in a further 96 260 women receiving IAP and the prevention of an additional 52 to 57 cases of EOGBS. This resulted in the prevention of three EOGBS deaths and four cases of severe disability. With screening, an additional 1675 to 1854 women receive IAP to prevent one EOGBS case and 24 065 to 32 087 receive IAP to prevent one EOGBS death.ConclusionsThe evidence base available for a broad range of model input parameters was limited, leading to uncertainty in the estimates produced by the model. Where data was limited, the model input parameters were agreed with the multidisciplinary stakeholder group, the first time this has been done to our knowledge. The main impact of screening is likely to be on the large group of low-risk women where the clinical impact of EOGBS tends to be less severe. This model suggests that the reduction in mortality and severe disability due to EOGBS with antenatal GBS screening is likely to be very limited, with a high rate of overdetection and overuse of antibiotics.

Re: Universal screening versus risk‐based protocols for antibiotic prophylaxis during childbirth to prevent early‐onset group B streptococcal disease: a systematic review and meta‐analysis

“…This is consistent with international guidelines and the screening pathway used in a study in London 5–7 . In the UK, the GBS model estimated that screening would not reduce the amount of IAP treatment offered to pregnant women, rather it would lead to 96 260 women receiving IAP in addition to those already treated within the risk‐based strategy alone 3 . Therefore, screening may do little to reduce IAP in women who have GBS risk factors, but it would introduce IAP in the group of predominantly low‐risk women who carry GBS at term.…”

“…It is important to ask what group B streptococcus (GBS) risk factors are included in a risk‐based strategy and whether pregnant women with these risk factors would be offered screening for GBS carriage and offered IAP if they have a negative GBS screening result in a universal screening strategy. In the UK context, an expert panel agreed that universal screening would be implemented in addition to risk‐based prevention and not as a replacement 3 . This is consistent with international guidelines and the screening pathway used in a study in London 5–7 .…”

“…The way in which the lack of unbiased evidence impedes assessment of screening is echoed in the systematic review's discussion and is also clearly something Walker et al's forthcoming randomised controlled trial (RCT) is seeking to address. That a reduction of early‐onset group B streptococcal disease (EOGBS) would be a likely outcome of the addition of screening to current UK risk‐based prevention guidelines is not disputed 3 . The nub of the UK NSC position is that the available evidence is insufficient to judge the balance of benefit and harm in the population which would be affected most by screening 4 …”

To screen or not to screen women for Group B Streptococcus (Streptococcus agalactiae) to prevent early onset sepsis in newborns: recent advances in the unresolved debate

“…The model proposed that the antenatal screening would have very limited effect on mortality and severe disability due to EOGBS and lead to excessive use of antibiotics. 24 Observational studies differ considerably in estimating the number of women who need to be given IAP to prevent a single case of EOGBS. In 2007, Angstetra et al in Australia reported the number of women needed to be given IAP was 1191 and 5704 women were screened to prevent one case of early-onset GBS disease.…”

Routine testing for Group B Streptococcus in pregnancy (GBS3 trial)

“…The sample size is based on the rate of all-cause early-onset neonatal sepsis between the routine testing and the risk factor based randomised strategies. The National Screening Committee model (23) This protocol is confidential and the property of the University of Nottingham. No part of it may be transmitted, reproduced, published, or used by others persons without prior written authorisation from the University of Nottingham testing to the risk factor strategy was estimated to result in 294-299 EOGBS infections, a relative risk ratio of 0.84.…”