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Can Fam Physician
Vol. 53, No. 6, June 2007, pp.1054 - 1055
Copyright © 2007 by The College of Family Physicians of Canada
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Research

Epidemiology of early-onset neonatal group B streptococcal infection

Implications for screening

Gerald Konrad, MD AAFP
Assistant Professor in the Department of Family Medicine at the University of Manitoba in Winnipeg, where he serves as Unit Director for the Family Medical Centre teaching unit

Alan Katz, MSc MB ChB CCFP
Associate Professor and Research Director in the Department of Family Medicine at the University of Manitoba and a Researcher at the Manitoba Centre for Health Policy

Correspondence to: Dr Gerald Konrad, Family Medical Centre, 400 Tache Ave, Winnipeg, MB M2H 3E1; telephone 204 237-2863; fax 204 231-2648; e-mail gkonrad{at}sbgh.mb.ca

Therapeutic interventions to prevent transmission of early-onset neonatal group B streptococcus (GBS) infection remain an issue for debate. No high-quality randomized prospective studies exist to guide our practice. It is unlike ly there will be a one-size-fits-all approach to prenatal GBS screening and intrapartum antibiotic prophylaxis.

Early-onset neonatal GBS infections are defined as GBS sepsis, meningitis, or pneumonia beginning at less than 7 days of life. Three approaches for preventing early-onset neonatal GBS infections have generally been used: universal screening of all pregnant women for GBS colonization, with intrapartum antibiotics given to those with positive results; universal screening of all pregnant women, with intrapartum antibiotics given only to those with positive results as well as other risk factors for GBS transmission; and intrapartum antibiotics for all women with risk factors for GBS transmission without prior screening.

Clinical risk factors for transmission are defined as results of a urine culture positive for GBS at any time during pregnancy, a previous infant with GBS infection, intrapartum fever (temperature, 38ºC or higher), preterm labour at less than 37 weeks, or prolonged rupture of membranes more than 18 hours.

While all 3 approaches for preventing early-onset neonatal GBS infections have previously been recommended, a 2002 landmark article by Schrag et al1 showed in a retrospective cohort study that universal prenatal screening for GBS was statistically superior to risk-based approaches for prevention. In light of these data, the US Centers for Disease Control and Prevention,2 the American College of Obstetricians and Gynecologists,3 and the Society of Obstetricians and Gynaecologists of Canada4 narrowed their recommendations to universal screening and intrapartum antibiotics for all GBS carriers to the exclusion of other strategies.

Professional organizations from other parts of the world, however, have questioned the movement to universal prenatal GBS screening. In 2003, the Royal College of Obstetricians and Gynaecologists in the United Kingdom recommended against offering antenatal GBS screening and promoted patient discussion regarding intrapartum antibiotic prophylaxis based on specific risk factors.5 In 2004, the New Zealand GBS Consensus Working Party recommended a risk-based prevention strategy over universal screening.6 Both of these groups developed their recommendations using smuch the same literature that guided the different recommendations of North American professional groups.

Universal screening for maternal GBS infection and intrapartum antibiotic prophylaxis of all colonized women might carry risks, including unexpected maternal penicillin anaphylaxis,7 an epidemiologic shift from gram-positive to gram-negative neonatal sepsis,8 changing resistance patterns among GBS and other organisms,9 and increased rates of other serious neonatal infections.10

Our study was designed to determine the degree of difference in outcome and antibiotic use between universal and risk-based approaches to prenatal GBS screening based on the epidemiology of early-onset GBS infection in Winnipeg, Man, and to examine the implications for GBS screening in our population.


   METHODS
TOP
 METHODS
RESULTS
 DISCUSSION
 Footnotes
 References
 
Our study comprised a retrospective chart audit of obstetric patients receiving intrapartum care in the Winnipeg region between April 1, 2001, and March 31, 2003. Ethics approval was obtained from the University of Manitoba Research Ethics Board as well as from the ethics boards of each of the 3 hospitals involved.

Randomly selected prenatal charts from each of the 3 Winnipeg hospitals providing intrapartum care during the study period were audited retrospectively. Data were collected for the presence or absence of prenatal GBS screening, the results of screening, the presence of clinical risk factors for neonatal GBS transmission, and use of intrapartum antibiotics to prevent neonatal GBS infection. Clinical risk factors for transmission were defined as noted earlier.

We also conducted a chart review of all cases of early-onset neonatal GBS infections treated at all hospitals providing neonatal intensive care during 2002 and 2003. Cases were determined using laboratory database searches for positive GBS cultures in infants younger than 7 days. These neonatal charts were audited for maternal risk factors for GBS transmission, history of maternal GBS screening and GBS status, use of maternal antibiotic prophylaxis, and neonatal outcome.

The Health Information Management Branch of Manitoba Health collected data about live births between April 1, 2001, and March 31, 2003 from the 3 Winnipeg hospitals providing intrapartum care. These data revealed 19 517 live births during the study period. Records of 330 women receiving perinatal care in the 3 regional hospitals between the same dates were reviewed. The quantity of charts from each hospital was weighted so as to match the percentage of births occurring in each hospital during the study period. A total sample size of 330 charts was chosen in order to obtain 95% confidence limits of ± 4% for the asymptomatic GBS carrier rate in Winnipeg, assuming a rate near 18% as previously reported.1


   RESULTS
TOP
 METHODS
 RESULTS
DISCUSSION
 Footnotes
 References
 
Of the 330 women whose charts were audited, 83% received GBS screening at least 48 hours before delivery. Results of GBS screening were not available for only 2 of these women. Positive GBS status among women in whom screening results were available was 26.1% (95% confidence interval 20.9%–31.3%).

Of the women with positive GBS status, 30% showed other clinical risk factors for neonatal GBS transmission. Of these, 86% received intrapartum prophylactic antibiotics. Of the 70% of GBS-positive women with no other clinical risk factors for GBS transmission, 84% were given intrapartum prophylactic antibiotics. Across the entire population of women studied, 19% demonstrated clinical risk factors for neonatal GBS transmission other than a positive result for GBS screening. Overall, 31% of women presenting for intrapartum care were treated with intrapartum antibiotics (Table 1).


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  		Table 1 Results of prenatal chart audits: N = 330.

 
Three cases of early-onset neonatal GBS disease were documented in Winnipeg between April 1, 2001, and March 31, 2003. All had positive results of blood cultures for GBS with negative results for cerebrospinal fluid. Two had maternal screening cultures positive for GBS while the third was documented as negative. Of the 2 cases with positive GBS status, 1 was not treated with intrapartum prophylactic antibiotics and the second was treated with a single dose before an imminent delivery. Other maternal risk factors for GBS transmission were absent in all cases. All 3 infants recovered without complications.


   DISCUSSION
TOP
 METHODS
 RESULTS
 DISCUSSION
Footnotes
 References
 
Our data showed that a substantial percentage of GBS carriers were otherwise asymptomatic. When a universal approach to screening is consistently applied, all of these asymptomatic GBS carriers would be screened and consequently treated with intrapartum prophylactic antibiotics. They would be overlooked, however, if a risk-based approach were used. If intrapartum prophylactic antibiotics were used in this group of women, how would it affect neonatal GBS outcomes? To answer this question, we must first determine the neonatal transmission rate among GBS carriers receiving no prophylactic antibiotics.

During the time period studied there were 19 517 births in Winnipeg. Projecting from our data, 26.1% (5093) of women in this group were GBS carriers, with 70.4% (3586) of them being otherwise asymptomatic. Of these asymptomatic GBS carriers, 16% (574) received no intrapartum prophylactic antibiotics. Because only 1 infant born to this group of asymptomatic GBS carriers developed early-onset neonatal GBS disease, the GBS transmission rate was 1.74 cases per 1000 live births to untreated GBS-positive women in the absence of other clinical risk factors. This is consistent with a transmission rate of 1.3 cases per 1000 previously reported.1

If 100 000 women in Winnipeg present for prenatal care, we project that 26.1% (26 100) will be GBS carriers (Table 2). Of these, 70.4% (18 374) will be asymptomatic. If they are managed using a risk-based approach, these 18 374 asymptomatic GBS carriers would deliver without intrapartum antibiotic prophylaxis (Figure 1).


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  		Table 2 Projected outcomes from universal screening and risk-based maternal GBS prophylaxis in Winnipeg, Man, region: N = 100 000.

 

Figure 10531054
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  		Figure 1 Projected outcomes from risk-based maternal GBS prophylaxis

 
With a transmission rate of early-onset neonatal GBS disease for untreated asymptomatic culture-positive women of 1.74 per 1000 live births, 32 infants from our group of 18 374 asymptomatic untreated GBS carriers would develop GBS disease using a risk-based approach.

Intrapartum prophylaxis has been previously shown to be 88.6% effective in preventing neonatal disease.1 Therefore, of these 32 infants, 29 will benefit from intrapartum antibiotic prophylaxis as applied with a universal screening strategy (Figure 2). While this number might seem significant, the absolute percentage of infants benefiting from universal screening and intrapartum antibiotic prophylaxis is very small. In fact, 3449 women (100 000÷29) would require universal screening to prevent a single case of early-onset neonatal GBS disease that would be missed using a risk-based approach (Table 3). The case-fatality rate for early-onset neonatal GBS infection has been previously reported at 5.0%.11 This being the case, the number needed to be screened increases to 68 966 to prevent a single death attributed to GBS.


Figure 20531054
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  		Figure 2 Projected outcomes from universal maternal GBS screening and prophylaxis

 

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  		Table 3 Number needed for universal screening to prevent a single neonatal GBS infection that would occur with risk-based screening

 
While these results are limited by the small number of cases, they are similar to those of larger studies. Applying these calculations to the much larger population reported by Schrag et al,1 we find that 4762 women need to be universally screened to prevent a single case of neonatal GBS infection that is missed using a risk-based approach. This number increases to 95 240 to prevent a single neonatal death attributed to GBS.

At a stable rate of 9700 births per year in the Winnipeg region, universally screening all women can be expected to prevent 3 cases of early-onset neonatal GBS infection each year that would be missed using a risk-based approach, and it would be necessary to apply universal screening to all prenatal women over the next 7 years to prevent a single neonatal death attributable to GBS.

When looking at our actual experience in Winnipeg, we find that universal screening would have potentially prevented 2 of the 3 documented cases of early-onset GBS disease, while a risk-based approach would have missed all 3. In other words, universal screening prevented 2 cases over a 2-year period that risk-based screening would have overlooked without affecting infant mortality. Also, neither strategy prevents neonatal GBS disease arising unpredictably from pregnancies without microbial or clinical risk factors for GBS transmission.

When employing a risk-based approach, the 19.1% of women presenting with clinical risk factors for GBS transmission will receive intrapartum prophylactic antibiotics. On the other hand, with a universal approach, the 26.1% of women who are GBS carriers will receive intrapartum antibiotics. This difference of 7 percentage points results in prophylactic exposure for 679 more women each year when a universal approach is employed rather than a risk-based approach. The costs of such an increase in antibiotic exposure, both financially and with regard to potential risks, are unknown.

In any population, these numbers depend on the underlying carrier rate of GBS relative to the rate of other risk factors for GBS transmission in that population. In the study by Schrag et al,1 there was no significant increased use of antibiotics among the universally screened women.

In another recent study,12 universal screening was actually favoured over a risk-based strategy to reduce the use of intrapartum antibiotics due to a low asymptomatic GBS carrier rate relative to the rate of other risk factors in that community. This clearly does not apply to our community.

Conclusion
Despite consistent recommendations in North America for universal screening for prenatal GBS colonization and treatment of all GBS carriers with intrapartum antibiotics to prevent early-onset neonatal GBS infection, the advantages gained by this approach over that of a risk-based approach in the Winnipeg region are small, with only 1 case prevented for 3449 women screened and 1 GBS-related neonatal death prevented for 68 966 women screened.

Much of the current literature points to a statistical improvement in neonatal GBS transmission when universal GBS screening is employed. However, in communities such as Winnipeg, where the rate of GBS transmission among untreated GBS carriers and the neonatal mortality associated with GBS disease are low, these benefits might not outweigh the uncertain costs of antibiotic exposure for all GBS carriers.

One of the foundation principles of family medicine is that the physician-patient relationship is of great importance. A patient-centred approach to care often necessitates involvement of the patient in the decision-making process. Consequently, in most clinical situations family physicians employ a strategy for screening and antibiotic prophylaxis based on informed patient discussion centring on identifying pertinent risks and benefits. It seems prudent that, when considering GBS screening for preventing neonatal GBS disease, we should maintain this standard in the care of our prenatal patients as well.



   EDITOR’S KEY POINTS
 
  • Universal screening for maternal group B streptococcus (GBS) infection and intrapartum antibiotic prophylaxis of all colonized women is currently the recommended standard of care in North America. Other jurisdictions have examined the same data and recommended a risk-based strategy.
  • The authors show that 3449 women would require universal screening to prevent a single case of early-onset neonatal GBS disease that would be missed using a risk-based approach; and that the number increases to 68 966 to prevent a single death.
  • Universal antibiotic prophylaxis might carry risks, including unexpected maternal penicillin anaphylaxis, an epidemiologic shift from gram-positive to gram-negative neonatal sepsis, changing resistance patterns among GBS and other organisms, and increased rates of other serious neonatal infections.
  • The authors suggest family physicians employ a strategy for screening and intrapartum antibiotic prophylaxis based on informed patient discussion centring on the identification of pertinent risks and benefits.

 


   Footnotes
TOP
 METHODS
 RESULTS
 DISCUSSION
 Footnotes
References
 
This article has been peer reviewed.

Contributors

Dr Konrad developed the concept and contributed to the design of the study; he collected and analyzed the data and prepared and revised the article for submission. Dr Katz contributed to concept and design of the study and reviewed, revised, and approved the article for submission.

Competing interests

None declared


   References
TOP
 METHODS
 RESULTS
 DISCUSSION
 Footnotes
 References
 

  1. Schrag SJ, Zell ER, Lynfield R, Roome A, Arnold KE, Craig AS, et al. A population-based comparison of strategies to prevent early-onset group B streptococcal disease in neonates. N Engl J Med 2002;347:233-9.[Abstract/Free Full Text]
  2. Schrag S, Gorwitz R, Fultz-Butts K, Schuchat A. Prevention of perinatal group B streptococcal disease. Revised guidelines from CDC. MMWR Recomm Rep 2002;51(RR-11):1-22.[Medline]
  3. American College of Obstetricians and Gynecologists. ACOG Committee Opinion: number 279, December 2002. Prevention of early-onset group B streptococcal disease in newborns. Obstet Gynecol 2002;100:1405-12.[Medline]
  4. Society of Obstetricians and Gynaecologists. The prevention of early-onset neonatal group B streptococcal disease. SOGC Clinical Guideline No. 149. J Obstet Gynaecol Can 2004;26(9):826-32.[Medline]
  5. Guidelines and Audit Committee of the Royal College of Obstetricians and Gynaecologists. Prevention of early onset neonatal group B streptococcal disease. Guideline No. 36, November 2003. London, Engl: Royal College of Obstetricians and Gynaecologists; 2003. Available from: www.rcog.org.uk/resources/Public/pdf/GroupB_strep_no36.pdf. Accessed 2007 Apr 15.
  6. Campbell N, Eddy A, Darlow B, Stone P, Grimwood K. New Zealand GBS Consensus Working Party. The prevention of early-onset neonatal group B streptococcus infection: technical report from the New Zealand GBS consensus working party. N Z Med J 2004;117(1200):U1023. Available from: www.nzma.org.nz/journal/117-1200/1023/. Accessed 2007 Apr 30.[Medline]
  7. Dunn AB, Blomquist J, Khouzami V. Anaphylaxis in labor secondary to prophylaxis against group B streptococcus. A case report. J Reprod Med 1999;44(4):381-4.[Medline]
  8. Hyde TB, Hilger TM, Reingold A, Farley MM, O’Brien KL, Schuchat A. Active Bacterial Core surveillance (ABCs) of the Emerging Infections Program Network. Trends in incidence and antimicrobial resistance of early-onset sepsis: population-based surveillance in San Francisco and Atlanta. Pediatrics 2002;110(4):690-5.[Abstract/Free Full Text]
  9. Mercer BM, Carr TL, Beazley DD, Crouse DT, Sibai BM. Antibiotic use in pregnancy and drug-resistant infant sepsis. Am J Obstet Gynecol 1999;181(4):816-21.[Medline]
  10. Glasgow TS, Young PC, Wallin J, Kwok C, Stoddard G, Firth S, et al. Association of intrapartum antibiotic exposure and late-onset serious bacterial infections in infants. Pediatrics 2005;116(3):696-702.[Abstract/Free Full Text]
  11. Centers for Disease Control and Prevention. Early-onset group B streptococcal disease—United States, 1998–1999. MMWR Morbid Mortal Wkly Rep 2000;49(35):793-6.
  12. Youden L, Downing M, Halperin B, Scott H, Smith B, Halperin SA. Group B streptococcal testing during pregnancy: survey of postpartum women and audit of current prenatal screening practices. J Obstet Gynaecol Can 2005;27(11):1006-12.[Medline]




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