toag.7.1.034.27040

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The Obstetrician& Gynaecologist

2005;7:34–39

Keywords

group Bstreptococcus,

intrapartumantibiotic

prophylaxis,neonatal sepsis

© 2005 Royal College of Obstetricians and Gynaecologists34

Introduction

Maternal colonisation

Group B streptococci (GBS) are facultatively

anaerobic, Gram-positive bacteria. They colonise

the rectum or vagina in approximately 28% of the

pregnant population,1 although their presence in

the genital tract tends to be transient or

intermittent rather than chronic.2 Carriage rates

vary between different countries and ethnic

groups,with rates as high as 41% being reported in

African American populations1,3 but rates as low as

12% being reported on the Indian subcontinent.4

For most women,GBS colonises the lower vagina

or rectum as an asymptomatic commensal

organism. Occasionally, however,clinical evidence

of maternal infection with GBS arises in the form

of urinary tract infection,5 chorioamnionitis6,7 or

postpartum endometritis.7 Maternal symptoms

tend to be mild, although systemic sepsis and

meningitis have been described.

Clinical features of perinatalinfection

When GBS colonisation occurs during

pregnancy, the fetus may be exposed in utero as

the bacterium ascends or as the fetus descends

through the genital tract. This process isfacilitated by the ability of GBS to adhere to

chorionic membranes,6 although infection is

more likely following prolonged membrane

rupture. Congenital pneumonia resulting in fetal

demise before or during labour is well

documented.8 More commonly, however,

clinical evidence of sepsis does not become

apparent until birth. Early-onset group B

streptococcal sepsis (EOGBSS) is defined as

presentation within the first 72 hours of life, the

majority of babies developing signs of infection

within a few hours of birth. Most babies with

EOGBSS present with nonspecific signs of

systemic infection including poor feeding,

lethargy and temperature instability. Pneumonic

and meningitic presentations are also common,

while rarer complications such as osteomyelitis

and septic arthritis are occasionally encountered.

All babies developing EOGBSS are at risk of

death or long-term neurodevelopmental

impairment and this is especially so for those

who develop meningitis (Figure 1).

GBS sepsis has been recognised as an important

cause of neonatal morbidity for over 30 years andis now known to be the most common serious

neonatal infection in the developed world. The

current UK prevalence of EOGBSS confirmed by

Group B streptococcaldisease: screening and

treatment in pregnancyBassel Abd El Malek, Nicholas D Embleton,Andrew D Loughney

Intermittent, asymptomatic colonisation of the vagina and rectum withgroup B streptococci is common in pregnancy. Vertical transmission ofthe bacterium from mother to fetus may lead to neonatal sepsis,characterised by pneumonia, meningitis and death in the most severelyaffected babies. Intrapartum prophylaxis with penicillin reduces the

burden of disease when given to women with risk factors for thedevelopment of group B streptococcal sepsis such as preterm labour,prolonged rupture of the membranes or maternal pyrexia in labour.Some professionals advocate the universal screening of all pregnantwomen for group B streptococci near term and the administration ofintrapartum antibiotic prophylaxis to all women testing swab-positive.This article summarises the salient features of group B streptococcaldisease and explores the rationale behind the use of intrapartumantibiotics for the prevention of neonatal infection.

10.1576/toag.7.1.034.27040 www.rcog.org.uk/togonline

Author details

Bassel Abd El Malek MRCOG, Specialist

Registrar in Obstetrics and

Gynaecology , Royal Victoria

Infirmary, Newcastle upon Tyne, UK.

Nicholas D Embleton MD MRCPCH,

Consultant in Neonatal Medicine,

Royal Victoria Infirmary, Newcastle

upon Tyne, UK.

Andrew D Loughney PhD MRCOG,

Consultant Obstetrician, The Royal

Victoria Infirmary, University of

Newcastle upon Tyne, RichardsonRoad, Newcastle upon Tyne NE1

4LP, UK.

email: andrew.loughney@nuth.

northy.nhs.uk

(corresponding author)

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© 2004 Royal College of Obstetricians and Gynaecologists

bacteriological culture is approximately 0.58 cases

per 1000 live births,9 although some authors

believe the true prevalence to be significantly

higher at around 3.6 per cases 1000 live births.10

Case fatality rates have improved in recent years,

with advances in neonatal care, but still stand at

between 4% and 10%, with higher rates

recognised for babies born prematurely.8 Seminalstudies in the USA in the mid-1980s were able to

show that the number of babies developing

EOGBSS could be reduced dramatically by

administering intrapartum antibiotic prophylaxis

to women, thereby decreasing bacterial

transmission to the fetus rather than treating fetal

infection itself.There are essentially two strategies

for the prevention of EOGBSS that have been

developed around this idea. In the ‘risk-based’

approach, intrapartum antibiotic prophylaxis is

given to any woman whose clinical history

suggests that her baby is at high risk of developingEOGBSS, such as a woman with prolonged

membrane rupture. In the ‘universal prenatal

screening’ approach, intrapartum antibiotic

prophylaxis is given to all women known to be

colonised with GBS, even in the absence of

clinically based risk factors.

The risk-based strategy

Risk factors for EOGBSS are well established and

have been confirmed in case–control studies

(Table 1).8 In addition, babies born to women

with a previously affected child are also at an

increased risk.11 The risk-based strategy requires

women with any one of these risk factors to be

given intrapartum antibiotic prophylaxis. The

strategy also allows for women with a positive

urine culture and women with a fortuitous finding

of GBS on any vaginal or cervical swab taken

during the index pregnancy to be treated. If these

criteria were strictly applied to the UK

population, at least 16% of women8,12 would

receive antibiotics in labour. It is estimated thatapproximately 625 women with one or more of

these risk factors would need to be treated to

prevent one case of EOGBSS, and one neonatal

death would be prevented for every 5882 women

treated.13

Although the number of women requiring

treatment in this scheme appears high, in 1996

the US Centers for Disease Control and

Prevention (CDC) published guidelines

accepting the risk-based approach as a viable

alternative for the prevention of EOGBSS.14

Theprinciple that a calculation of risk should be used

to inform maternal choice was later endorsed by

the Public Health Laboratory Service (PHLS)

GBS Working Group in the UK15 and forms the

basis of advice given in the present RCOG

Guideline.12 Subsequent experience in the USA

confirmed that, when rigorously applied,

intrapartum antibiotic prophylaxis given to

women with risk factors for EOGBSS could

deliver a clear reduction in neonatal morbidity

and mortality.16,17 Reflecting this, implemen-

tation of the risk-based treatment strategy

measurably reduced high-dependency neonatal

special care cot occupancy in US states

implementing the strategy. Given the high cost

35

Figure 1. Outcome

following maternal group

B streptococcal

colonisation

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of neonatal intensive care and supportive

treatments such as extracorporeal membrane

oxygen, a similar experience in the UK might

effectively make the exercise cost neutral to the

NHS.

While this approach has many advocates,

30–40% of babies with EOGBSS are born towomen with no identifiable risk factors. Even

rigorous application of the risk-based strategy

cannot, therefore, reduce the incidence of

EOGBS by more than 60–70%. Experience

from the USA suggests that this is true in

practice, leading the CDC to publish guidelines

backing the potentially more effective alternative

strategy of universal prenatal screening.17

Universal prenatal screening

The 2002 CDC guidelines recommended

bacteriological screening for all pregnant women

and the use of intrapartum antibiotic prophylaxis

for all screen-positive women, regardless of the

presence or absence of other risk factors for

EOGBSS. To achieve this, low vaginal and

endoanal swabs must be taken at 35–37 weeks of

gestation. This relatively late gestation is

necessary because the positive and negative

predictive values of swabs taken more than 5

weeks before delivery are insufficiently high inmost populations to guide treatment.

Since the site of colonisation does not influence

the decision to use intrapartum antibiotic

prophylaxis, screening can be performed by

passing a swab into the lower part of the vagina

then passing the same swab into the anus before

placing it in culture medium.Separate swabs may

also be used, but both swabs should then be

placed into the same culture medium so that a

single bacteriological report is generated. Studies

have shown that, with appropriate instruction,most pregnant women can take their own swabs,

improving the acceptability of the procedure

without affecting its sensitivity.18 A sample of

urine should also be analysed in the third

trimester, since GBS bacteriuria is associated with

exposure of the fetus to a high bacterial load.19

For screening to be effective, a method of

culture must be employed that is both sensitive

and specific. Standard bacteriological swabs

plated directly on to agar fail to detect GBS inup to 50% of colonised women. In contrast, by

placing swabs directly into a selective enriched

broth,20 the assay sensitivity can be increased

dramatically.

Some babies exposed to GBS will develop early-

onset disease even after optimal antibiotic

prophylaxis, particularly when infection has

arisen in utero.21 Nevertheless, US states

employing the screening strategy have reported a

reduction in rates of EOGBSS of up to 86%, a

decline that is significantly better than that foundin states following the risk-based strategy.17

In the UK, implementation of a universal

prenatal screening policy would impact

significantly upon the provision of antenatal care.

The organisational challenge of obtaining and

processing swabs from a large number of women

and ensuring that results are available to care

providers during labour would be considerable.

The screening system would also have to comply

with the NICE guidelines on the provision of

routine antenatal care.22 Access to written

information and personal, professional advice

would be needed before swabs were obtained,

when results were available and prior to

instituting antibiotic prophylaxis. While these

requirements could be met in the course of

present antenatal care arrangements for most

women, some additional time allocation would

inevitably be required to fulfil the counselling

obligations attendant to the screening

programme.

Although the National Screening Committee in

the UK is currently considering adoption of theuniversal screening approach,this is unlikely to be

their favoured option because it would almost

certainly lead to the treatment of more women

with intrapartum antibiotic prophylaxis than

would adoption of the risk-based approach, with

up to 30% being offered antibiotics in labour.23

The finding of a positive swab would also impact

upon the woman’s care in labour in a wider sense,

influencing the woman’s decision regarding place

of confinement and possibly colouring clinicians’

views when choosing management options in

labour. Furthermore, the cost implications of universal prenatal screening would be significant,

even though a reduction in usage of high-

dependency neonatal care might be expected to

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Table 1. Risk factors for early onset group B streptococcal disease; from

Oddie and Embleton8

95% confidenceFactor Odds ratio interval

Preterm birth 37 weeks 10.4 3.9–27.6Preterm birth 34 weeks 33.6 4.0–283.3

Rupture of the membranes 25.8 10.2–64.818 hours

Preterm prolonged rupture 30.3 6.3–144.5

of the membranesIntrapartum fever 38C 10.0 2.4–40.8Any antenatal maternal 17.7 1.9–163.5

culture of GBSPreviously affected child Presently

unquantified

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offset these costs to some degree. Perhaps, more

pertinently, the balance may lie between the

inconvenience to the mother and to the health

service of implementing a screening programme,

set against achieving the maximum possible

reduction in neonatal morbidity and mortality.

Combining universal prenatalscreening and the risk-basedstrategy

The Canadian Task Force on Preventative Health

Care has shown that by adopting a universal

screening strategy but then only offering

intrapartum antibiotic prophylaxis to women

who test swab-positive and who have additional

risk factors for EOGBSS, the number of women

treated with penicillin in labour can be reduced

to as little as 3.4%.24 Although this approach is

likely to cause less morbidity in labouringwomen by reducing antibiotic usage, it retains

the financial and organisational obstacles

inherent in implementing a universal antenatal

screening programme and has the potential to

reduce the incidence of EOGBSS by only a little

over 50%.25 Because of these limitations, the

approach is rarely encountered in UK or US

practice.

Chemoprophylaxis and therapy

Intrapartum antibiotic prophylaxis

Several studies have confirmed the efficacy of

intrapartum antibiotic prophylaxis for EOGBSS

prevention, with most concluding that the use

of antibiotics significantly reduces the rate of

neonatal colonisation and sepsis.16,25 To be

effective, it may be necessary for drug

administration to commence 4 or more hours

before delivery, since efficacy increases with

both the length of time the fetus has been

exposed to antibiotics in labour and the number

of doses administered. This 4-hour rule shouldnot be adhered to dogmatically, since clear

evidence defining the minimum necessary time

exposure to intrapartum antibiotic prophylaxis

to achieve neonatal benefit is lacking.16,26

To date, there has been no reported resistance of

GBS to either penicillin or ampicillin in vivo and

virtually no resistance in vitro. Since ampicillin

has a relatively broad spectrum of antimicrobial

activity, its widespread use has the potential to

select for resistant organisms. Because of this,

penicillin remains the drug of choice for intrapartum antibiotic prophylaxis, given at an

intravenous dose of 3 g (5 MU) initially then 1.5 g

(2.5 MU) 4-hourly until delivery.

As much as 10% of the UK population claims to be

allergic to penicillin. Although true allergic

reactions probably occur in less than 1%,

anaphylaxis has been reported in women receiving

intrapartum antibiotic prophylaxis for GBS27 and

might be expected to arise in 1/100 000 women

treated.28 The RCOG estimates that, if a universal

screening policy were adopted leading to theadministration of intrapartum antibiotic

prophylaxis to 30% of parturients, two anaphylaxis-

related maternal deaths could be expected annually

in the UK.12 In the search for a suitable alternative

antibiotic, up to 25% of GBS isolates have been

found to be resistant to erythromycin, which also

fails to achieve bactericidal levels in the amniotic

fluid. Up to 15% are resistant to clindamycin, the

currently recommended second-line drug in the

UK.12 First-generation cephalosporins such as

cefazolin may be more effective and have the

advantage of achieving high intra-amnioticconcentrations while retaining a relatively narrow

spectrum of antimicrobial activity.

In theory, the widespread use of intrapartum

antibiotic prophylaxis could lead to an increase in

the incidence of early-onset non-GBS sepsis in

neonates, negating any beneficial effect.Clinicians

might also expect to encounter an increase in the

prevalence of drug-resistant bacteria causing

disease. In reality, these phenomena have rarely

been observed and some centres following CDC

guidelines have actually recorded a fall in the

incidence of non-GBS sepsis.17 To preserve this

advantage, however, the use of antibiotics with a

broad spectrum of activity should be reserved for

women with true penicillin allergy and close

surveillance should be kept of the range of

bacteria causing neonatal disease.

Treating the neonate

Combining infant antimicrobial prophylaxis (100

mg/kg intravenous penicillin given daily in two

divided doses)15 with intrapartum antibiotic

prophylaxis reduces the rate of EOGBSS in bothterm and preterm infants when compared with a

strategy of no intervention29 but such routine

neonatal prophylaxis has not gained wide support

and its benefits remain uncertain.At present, the

PHLS, RCOG and CDC recommend that, in

general, whether concern arises because of the

presence of maternal risk factors or maternal

swab results, babies who have received

intrapartum antibiotic prophylaxis before birth

require heightened observation alone for 12–48

hours after delivery, with intravenous penicillin

reserved for babies developing signs of disease.15,17 As exceptions to this rule, penicillin

should also be considered for babies who are

otherwise well but who have a combination of

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risk factors such as maternal GBS bacteriuria in

the presence of prolonged membrane rupture.

Most paediatricians also treat babies born to

mothers with unequivocal features of

chorioamnionitis, babies with twin siblings

affected by EOGBSS and babies with siblings

who have had previously confirmed EOGBSS.

Obstetric issues

The risk of fetal infection in women with intact

membranes who are not in labour is low.

Because of this, antibiotic cover for GBS need

not be administered routinely to women

undergoing an elective caesarean section, even in

the presence of positive swabs. A dilemma may

arise when, for example, a woman who is swab

positive or has EOGBSS risk factors and who is

due to be delivered by caesarean section presents

with rupture of the membranes or in labour. Inthese circumstances, GBS cover may be given,

accepting that delivery is likely to take place

below the theoretical 4-hour prophylaxis

threshold. Delaying delivery to achieve this

threshold would be illogical, since fetal bacterial

exposure increases with time.

Standard obstetric practice dictates that some

women with positive GBS swabs or risk factors for

neonatal sepsis will undergo one of a number of

common obstetric interventions during the course

of pregnancy and labour.For example,induction of

labour is as likely in this group of women as in the

general population.There is no present evidence to

suggest that antenatal vaginal examination,

membrane sweeping or insertion of prostaglandin

pessaries for labour induction increase the rate of

transmission of GBS from the mother to the fetus.

In labour,although neonatal infection rates increase

in association with the frequency of vaginal

examinations and the placement of fetal scalp

electrodes, cause and effect have not been proven in

these circumstances. Furthermore, there are few

data available specifically relating GBS sepsis to

these intrapartum procedures. There is, therefore,no clear evidence to suggest that women whose

babies are at risk of EOGBSS should receive

anything other than normal obstetric or midwifery

care in labour in addition to antibiotic prophylaxis.

Issues relating to infants bornprematurely

Approximately 6% of women give birth after

spontaneous labour before 37 weeks of

gestation and, of these, one-third give birth

before 32 weeks.30 Premature babies are atparticularly high risk of developing EOGBSS

and they are also more likely to die or develop

long-term sequelae as a result. The CDC

recommends administration of intrapartum

antibiotic prophylaxis to all women who seem

likely to give birth because of preterm labour,

regardless of the presence of membrane

rupture, while the PHLS and the RCOG

concur that intrapartum antibiotic prophylaxis

should be considered in this group.12 When

tocolytics are used in an attempt to arrestlabour, low vaginal and rectal swabs should be

taken to determine the woman’s colonisation

status, although reliable results may not be

available in time to influence the use of

antibiotic prophylaxis.After delivery, continued

treatment with penicillin is essential for babies

showing signs of infection. In practice, signs of

infection are frequently non-specific and it is

also impossible readily to distinguish

surfactant-deficient lung disease from

congenital pneumonia, so it is common for

preterm babies to receive antibioticsimmediately after delivery.

Future perspectives

Rapid detection of GBS

Because of the transient or intermittent pattern

of maternal colonisation normally encountered,

an intrapartum assay for GBS could hold a

significant advantage over an earlier screening test

by more accurately reflecting the colonisation

status of a woman in labour. For this, an assaywould be required that could provide a result

rapidly, that was highly sensitive to the presence

of GBS and that was sufficiently specific to give a

low false-positive result rate. Such a test would

also allow the accurate assessment of women

presenting with threatened preterm labour and

preterm rupture of the membranes.

A number of GBS rapid detection kits are

commercially available but, for many, their

sensitivity is too low to allow effective

intervention based on their results.31,32 A new

polymerase chain reaction assay has been studied,

which is sensitive to the presence of GBS in 97%

of cases and claims 100% specificity.33

Furthermore, assay results are available within 45

minutes. The assay is not, however, currently

commercially available so a true analysis of benefit

remains to be determined.

Immunisation

Maternal immunisation against GBS prior to or

during pregnancy has the potential to prevent

fetal colonisation in utero, thereby eliminatingGBS-mediated stillbirth in addition to

EOGBSS. It could also impact significantly on

late-onset disease firstly by reducing vertical

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transmission of the bacterium and secondly by

providing the neonate with passive immunity

against infection acquired ex utero. At least eight

different GBS serotypes exist, based upon the

specific structure of the capsular polysaccharide

and embedded proteins.Although only three or

four serotypes are responsible for the majority of

disease, a vaccine would nevertheless have to bemultivalent to be effective. Current phase one

and two clinical tr ials have generally investigated

the use of monovalent vaccines, with limited

potential for widespread disease prevention.34

Conclusions

In order to meet the challenge of reducing

morbidity and mortality caused by group B

streptococcal disease after birth, the RCOG has

proposed that a woman should be offered

intrapartum antibiotic prophylaxis based upon

maternal risk factor assessment.12 This contrasts

with the current US CDC strategy based upon the

use of universal prenatal screening. It is likely that

the former policy will be cheaper to implement,

easier to administer and less likely to impact

adversely upon a woman’s care in labour,while the

latter would possibly deliver greater reductions inneonatal disease. In the future, rapid assays for

maternal GBS colonisation may be available for

use in labour while vaccination against GBS

represents the greatest hope of reducing the

burden of neonatal and maternal disease. While

GBS remains the most prevalent organism causing

early-onset infections, it should be remembered

that more than 50% of early-onset infections are

caused by non-GBS organisms,35 so the

eradication of EOGBSS should not be seen as the

endpoint in combating neonatal sepsis. ■

39

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