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Prevention of perinatal group B streptococcal disease: screening practice in public hospitals in Victoria

Mary Connellan and Euan M Wallace
Med J Aust 2000; 172 (7): 317-320.
Published online: 3 April 2000
Research

Prevention of perinatal group B streptococcal disease: screening practice in public hospitals in Victoria

Mary Connellan and Euan M Wallace

MJA 2000; 172: 317-320
For editorial comment, see Oats

Abstract - Introduction - Methods - Results - Discussion - Acknowledgements - References - Authors' details
- - More articles on Infectious diseases and parasitology


Abstract Objectives: To survey clinical protocols for prevention of early-onset group B streptococcal disease (EOGBSD) of the newborn in public maternity hospitals.
Design: Postal questionnaire with telephone follow-up when required.
Setting: All hospitals that undertook deliveries in public patients in the State of Victoria, November 1997 to January 1998.
Results: The survey was sent to 84 hospitals: 71 responded and 64 met the criteria and provided usable data (76% response rate). These 64 represented 42 784 births (68% of births in Victoria in 1996). Most hospitals (62; 97%) undertook actions that would identify and treat pregnant women at risk of EOGBSD. 48 (75%) performed bacteriological screening for maternal GBS carriage, but only 20 of these had a unified protocol. Screening was mostly by low vaginal swab (15 hospitals) and before 30 weeks' gestation (12 hospitals). Low vaginal swab plus anal swab was used in only one hospital. Bacteriological screening was significantly more common in metropolitan hospitals than in rural hospitals (100% versus 67%; P = 0.007, Fisher's exact test). Targeting of prophylaxis by recognised risk factors was reported by 59 (92%) hospitals, 45 of which also undertook screening. There was considerable variation in the specific risk factors used.
Conclusions: While there was clearly widespread awareness of EOGBSD in Victorian public hospitals, prevention programs varied considerably. The development of consensus practice guidelines might improve EOGBSD prevention, reducing morbidity, mortality and costs.


Introduction Since the 1970s, group B streptococci (GBS) have been recognised as a major cause of neonatal systemic infection in the first week of life -- so called early-onset group B streptococcal disease (EOGBSD). The reported incidence of this condition varies between 1 and 4 per 1000 livebirths.1 Infants acquire the infection by vertical transmission from an asymptomatic mother during delivery.2 Clinical disease manifests at birth or within 24-48 hours as pneumonia, septicaemia or, less commonly, meningitis.1

In Australia, the prevalence of GBS vaginal carriage has been estimated at 12%-15%,3-5 and about 1%-2% of infants born to women carrying GBS develop EOGBSD, with about 6% of cases being fatal.2,5-7The risks of EOGBSD and death are particularly high in preterm infants.2 However, antibiotic prophylaxis given to "at risk" women during labour has been shown to significantly reduce the incidence of EOGBSD, and is an important and worthwhile public health measure.2,7-9

While the value of prophylactic antibiotic intervention in at-risk women is now widely agreed, the best means of targeting these women is perhaps less clear. Comprehensive reviews of the available evidence have been published both in Australia1,5,10 and overseas.2,11-13 There are two broad approaches to targeting prophylaxis -- identification of GBS carriers by bacteriological screening or treating by clinical risk factors.

No trials have compared the efficacy of the two approaches. It is therefore perhaps not surprising that, anecdotally, GBS intervention practices differ greatly between public hospitals across the State of Victoria. However, no objective data are available to assess the extent of these differences and the appropriateness of current practice.

We surveyed all public maternity hospitals in Victoria to explore what GBS intervention programs were in place and, in particular, to assess whether practice was in line with currently available evidence.


Methods The Victorian Perinatal Data Collection Unit, Melbourne, provided contact details of all maternity hospitals in Victoria and identified those that undertook deliveries in public patients. Between November 1997 and January 1998, a six-page survey form containing 18 questions was sent to the Delivery Suite Nursing Unit Manager, or equivalent, in each of these hospitals. The survey was multiple-choice format with some free-text fields. Non-respondents were sent a second copy of the survey form two months later and were telephoned if necessary.

Data on deliveries in 1996 were supplied by the Victorian Perinatal Data Collection Unit. Statistical analyses were performed using Statview 4.1.14 Significance was taken as P < 0.05.


Results Of the 84 hospitals surveyed, 71 responded and 64 met the criteria and provided usable data, giving a final response rate of 76% (three respondents delivered only private patients, one cared for postnatal women only, and three did not provide GBS screening information). The 64 hospitals that provided usable data accounted for 42 784 births in 1996 (68% of all births and 93% of all births to public patients in Victoria) and comprised 16 hospitals in metropolitan Melbourne and 48 rural hospitals.

Of the 64 hospitals, 62 (97%) reported undertaking procedures that would identify and treat at least some women with a baby at risk of EOGBSD; 48 hospitals (75%) undertook routine antenatal screening for maternal GBS carriage, including 45 which also offered antibiotic prophylaxis on the basis of risk factors. Another 14 hospitals (22%) used the latter approach alone.

Screening for GBS
The hospitals which undertook routine antenatal bacteriological screening accounted for 97% of all deliveries in the 64 responding hospitals. They comprised all 16 metropolitan hospitals and 32 of the 48 rural hospitals, a significant difference in proportions between metropolitan and rural hospitals (P = 0.007, Fisher's exact test).

Of the 48 hospitals that undertook screening, 20 had a unified hospital screening protocol, with the remainder using individual-doctor protocols. The 20 with a unified protocol comprised nine of the 16 metropolitan hospitals and 11 of the 32 rural hospitals (P = 0.22, Fisher's exact test).

Characteristics of the screening protocols among these 20 hospitals are shown in Box 1. Most protocols (65%) were less than five years old, and 40% were less than two years old. The most common approach to bacteriological screening was to perform a low vaginal swab only (15 of 20 hospitals), or, less commonly, a high vaginal swab only (four hospitals). Only one hospital performed a low vaginal swab combined with an anal swab. All but one hospital screened only once in the pregnancy, either before 30 weeks' gestation (12 hospitals) or between 30 and 34 weeks' gestation (seven). The hospital that screened more than once did not specify gestations. All hospitals that performed bacteriological screening administered intrapartum antibiotics to all women who were GBS-positive.

Screening of private patients
Bacteriological screening was offered to private patients by some or all obstetricians at 37 of the 64 hospitals. This was a smaller proportion of hospitals than offered screening to public patients, although the difference did not reach significance (P = 0.06, Fisher's exact test). In only 18 of these 37 hospitals did all obstetricians offer screening to their private patients. In 13 hospitals, none offered screening to private patients, and in 14 the respondent did not know if it was offered.

Risk-factor-targeted prophylaxis
Targeting of prophylaxis by recognised clinical risk factors was reported by 59 of the 64 hospitals (92%). Criteria used are shown in Box 2. Antibiotics were reported to be given most commonly for clinical signs of intrapartum infection (51 hospitals) and pre-labour rupture of the membranes (43 hospitals), although the time from membrane rupture to starting antibiotic administration varied considerably. Only 10 hospitals administered antibiotics to women admitted in preterm labour below a specified gestation. All were metropolitan hospitals that also performed routine bacteriological screening. Only four hospitals (6%) administered antibiotics on the basis of all five recognised criteria. Two of these also undertook screening.

With regard to the antibiotic used as chemoprophylaxis, 14 of the 20 hospitals with a unified protocol used penicillin, four amoxycillin and two ampicillin. The 14 hospitals using penicillin all had different treatment regimens. Of the hospitals that lacked a unified protocol, only four reported the antibiotic regimen used -- penicillin in three and amoxycillin in one.


Discussion To our knowledge, this is the first survey of GBS screening practices in pregnancy to be reported in Australia. It reveals that prenatal screening and prophylaxis for GBS infection were widely practised in public hospitals in Victoria. However, the specific strategies varied considerably, and, while this variation is understandable (given the lack of robust comparative data for the various possible approaches2,10,12,15), it translated into a less than ideal approach in many centres.

Current evidence suggests that the optimum approach to reduce EOGBSD is to offer intrapartum chemoprophylaxis, using penicillin (or erythromycin in women allergic to penicillin) to at-risk mother-infant pairs. These at-risk pairs are identified by bacteriological screening, involving a low vaginal and anal swab performed at 36-38 weeks' gestation and/or by clinical risk factors (Box 3).2,10

In our survey, most hospitals reported targeting prophylaxis through bacteriological screening. However, the varied approaches to this screening revealed that current practice may not be as effective as possible. In addition, while most hospitals undertook screening, only 20 had a unified protocol, while the remaining 28 reported that protocols differed between doctors. This, together with the variable practice for private patients, suggests that it may be useful to develop more uniform Australian guidelines. Indeed, that only two hospitals (3% of respondents) reported a current protocol that would be expected to maximally prevent EOGBSD (targeting prophylaxis by bacteriological screening and by all risk factors shown in Box 3) suggests that the introduction of uniform practice guidelines would be worthwhile.

The most common differences between the reported screening protocols and an approach expected to minimise EOGBSD were the maternal sites sampled and the timing of screening. GBS carriage within individuals is not constant. Consequently, bacteriological swabs taken at 28 weeks' gestation have only a 50%-70% positive predictive value for carriage at delivery, while about 5%-10% of women who are GBS-positive at delivery are negative at 28 weeks.3,13,16 Therefore, the closer to delivery that bacteriological screening is undertaken, the greater its utility, both as sensitivity and specificity are increased,2,10,16 and as the costs of screening are saved for the 5% of pregnant women who deliver preterm (and should receive prophylaxis irrespective of the screening result.2,11). Thus, bacteriological screening is probably best undertaken at 36-38 weeks' rather than at less than 30 weeks' gestation, the most popular time in our survey.

Nevertheless, despite these theoretical considerations, a significant reduction in the incidence of EOGBSD was recently reported by King George V Hospital, Sydney, where screening is performed at 28 weeks' gestation.17 This result emphasises that bacteriological screening at 28 weeks' gestation is preferable to no screening at all.

Detection of GBS is increased by 5%-25% if an anal swab is collected in addition to a vaginal swab.16,18,19 Only one hospital in our survey reported collecting both swabs; most took only a low vaginal swab. It has been suggested that Australian women would find collection of anal swabs unacceptable,20 but no objective evidence has been presented for this. Furthermore, most United States centres surveyed by the Centers for Disease Control took anal swabs,21 suggesting that the practice may be more acceptable than is assumed. It would certainly be worthwhile asking Australian women, and reappraising the method of screening most appropriate for our population. Collection of high vaginal swabs, reported by four hospitals in our survey, is inappropriate for GBS screening.

The most cost-effective approach to preventing EOGBSD is to offer antibiotic prophylaxis to women with identified risk factors, without bacteriological screening.15 This approach has been recommended by some Australian groups (Professor James King, Mater Perinatal Epidemiology Unit, Mater Misericordiae Mothers' Hospital, Brisbane, Qld, personal communication). Most hospitals surveyed (92%) offered prophylaxis on the basis of risk factors, but only four (6%) used all recognised risk factors appropriately (Box 3). As the relative risk of EOGBSD is significantly greater in preterm neonates than in babies born at term,7 any EOGBSD prevention program should ideally include intrapartum prophylaxis for any woman labouring before 37 weeks' gestation, irrespective of whether she was screened earlier in pregnancy or of the result of that screening.2,11 It was disappointing that only a minority of the hospitals surveyed had such a policy, particularly as infection per se is a major recognised cause of preterm labour. That no rural hospital had such a policy may reflect that these hospitals transfer such women for level 3 neonatal care, and that preparation for transfer focuses more on tocolytic therapy and corticosteroid prophylaxis. If so, then an educational campaign to encourage early antibiotic treatment instituted at the referring hospital might be worthwhile.

We were also surprised that only a few hospitals offered antibiotic prophylaxis to women who had had a previous baby with EOGBSD. Neonatal EOGBSD is a devastating infection, and, in our experience, parents who have had an infected child usually seek interventions to prevent infection in a future delivery. That most clinicians and hospitals do not routinely offer prophylaxis in this situation suggests a lack of awareness that this history is an important risk factor. Similarly, the variable responses to the other accepted risk factors suggest that a significant proportion of health providers are either unaware of the epidemiology of EOGBSD or do not perceive EOGBSD as an important clinical problem.

Our survey of Victorian public hospitals showed that, while most are clearly aware of EOGBSD, only a minority currently have a strategy that maximises prevention of EOGBSD and represents most cost-effective practice. However, very minor changes in practice would be expected to improve EOGBSD prevention and significantly reduce costs,15 for both screening and treatment. Accordingly, our data support the case for a comprehensive, statewide, or possibly national, education program, and for the development and introduction of uniform consensus practice guidelines.



Acknowledgements
The authors would like to thank the participating hospitals as well as Dr Jane Halliday and Ms Sofia Mercer, from the Victorian Perinatal Data Collection Unit. EMW was partly funded by a Charles and Sylvia Viertel Clinical Investigator Fellowship.

Disclosure: We are not aware of any conflict of interest arising from performing or reporting this work.


References
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  13. Regan JA, Klebanoff MA, Nugent RP, et al, VIP Study Group. Colonization with group B streptococci in pregnancy and adverse outcome. Am J Obstet Gynecol 1996; 174: 1354-1360.
  14. Statview 4.1. Berkeley, CA: Abacus, 1994.
  15. Garland SM, Kelly N. Early-onset group B streptococcal sepsis: economics of various prevention strategies. Med J Aust 1995; 162: 413-417.
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  17. Jefferey HE, Lahra MM. Eight-year outcome of universal screening and intrapartum antibiotics for maternal group B streptococcal carriers. Pediatrics 1998; 101: E2.
  18. Badri MS, Zawaneh S, Cruz AC, et al. Rectal colonisation with group B streptococcus: relation to vaginal colonisation of pregnant women. J Infect Dis 1977; 135: 308-312.
  19. Dillon HC, Gray E, Pass MA, Gray BM. Anorectal and vaginal carriage of group B streptococci during pregnancy. J Infect Dis 1982; 145: 794-799.
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(Received 10 Nov 1999, accepted 14 Feb 2000)



Authors' details
Monash Medical Centre, Melbourne, VIC.
Mary Connellan, RM, MPH, Midwife, Women's Health Program, Southern Healthcare Network;
Euan M Wallace, MD, FRACOG, Senior Lecturer, Department of Obstetrics and Gynaecology, Monash University.

Reprints: Dr E M Wallace, Department of Obstetrics and Gynaecology, Monash University, Monash Medical Centre, 246 Clayton Road, Clayton, VIC 3168.
euan.wallaceATmed.monash.edu.au


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1: Characteristics of screening for group B streptococcus in 20 hospitals with a unified screening protocol
Number of hospitals

Years since screening protocol introduced
  < 28 (40%)
  2-55 (25%)
  > 5-91 (5%)
  > 92 (10%)
  Not known4 (20%)
 
Form of screening
  Low vaginal swab only15 (75%)
  High vaginal swab only4 (20%)
  Low vaginal swab and anal swab1 (5%)
 
Frequency per pregnancy
  Once only19 (95%)
  More than once1 (5%)
Timing
  < 30 weeks' gestation12 (60%)
  30-34 weeks' gestation7 (35%)
  Unknown1 (5%)*

*The hospital that screened more than once did not specify gestations.
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2: Criteria for intrapartum administration of antibiotics in 64 hospitals in Victoria
 
CriteriaNumber of hospitals using

Clinical signs of intrapartum infection51 (80%)
Pre-labour rupture of membranes43 (67%)
  < 6h4 (6%)
  6-12h0
  > 12-18h10 (16%)
  > 18-24h4 (6%)
  > 24h21 (33%)
  Doctor-dependent4 (6%)
Previous GBS-affected baby30 (47%)
GBS-positive vaginal swab in previous pregnancy22 (34%)
Preterm labour10 (16%)
  Gestation < 37 weeks7 (11%)
  Gestation < 34 weeks2 (3%)
  Gestation < 32 weeks1 (2%)

GBS=Group B streptococcus.
Back to text

 
3: Key risk factors for early-onset neonatal group B streptococcal disease (EOGBSD)

  • Preterm delivery
    (< 37 weeks' gestation)
  • Prolonged rupture of membranes (> 18h)
  • Previous infant with EOGBSD
  • GBS bacteriuria during pregnancy
  • Intrapartum maternal pyrexia
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Received 14 November 2018, accepted 14 November 2018

  • Mary Connellan
  • Euan M Wallace


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