Maternity Care Calendar and Guidelines: Prevention of Group B Streptococcal Infection in Newborns

Background:

Group B streptococcal (GBS) infection is a significant cause of neonatal morbidity and mortality. It became the leading cause of neonatal morbidity and mortality in the U.S. in the 1970's. [1] 10-30% of women are colonized with GBS.[2] Before the use of intrapartum antibiotics was common, the incidence of invasive GBS disease in newborns was 2-3 per 1000 live births. The incidence in 1990 in the U. S. was 1.8 cases per 1000 live births (1.5 /1000 for early-onset and 0.35/ 1000 for late onset)[1] In 1999 the incidence had dropped to 0.5 cases per 1000 live births.

Summary of Evidence:

Canadian Task Force on Preventive Health Care: A recent update by the Canadian Task Force on Preventive Health Care (CTFPHC) on the prevention of Group B streptococcal infections in newborns can be found on their website. [3] ( www.ctfphc.org )

In their report, the CTFPHC found that none of the randomized clinical trials evaluating the effectiveness of universal screening for GBS colonization followed by intrapartum chemoprophylxis (IPC) for all colonized women or selective IPC for women with risk factors showed a statistically significant reduction in the incidence of early-onset neonatal infection. None of these studies had the power to show a significant difference, but they did show a trend toward reduction.[3] However,there is cumulative evidence from cohort studies that either universal screening followed by selective IPC for colonized women with risk factors or universal screening followed by IPC for all colonized women is effective in preventing early-onset GBS in newborns. [3]

Therefore they recommend:

universal screening for GBS colonization at 35-37 weeks' gestation followed by selective IPC given to women with risk factors*. "This appears to be the most efficient strategy." (grade B recommendation, level II-1, II-2 evidence)

or
universal screening for GBS at 35-37 weeks' gestation followed by IPC of all colonized women. (grade B recommendation, level II-2 evidence)

The efficacy for IPC on the basis of risk factors alone has not been studied. Therefore the CTFPHC states that:
there is insufficient evidence to recommend for or against the risk factor strategy to reduce early onset neonatal disease (grade C recommendation).

*risk factors include:

preterm labour (<37 weeks gestation)
prolonged rupture of membranes (>18 hours)
maternal fever > 38.0 C
group B strep bacteriuria during pregnancy
previous delivery of an infant with GBS disease regardless of current GBS colonization

Collection of antenatal cultures (swab from lower vagina and rectum) should occur at 35-37 weeks gestation.
Intrapartum chemoprophylaxis consists of at least 1 dose of intravenous penicillin (5 million units) given at least 4 hours prior to birth. If labour continues beyond 4 hours then penicillin (2.5 million units) should be administered every 4 hours until delivery. For women allergic to penicillin, clindamycin 900 mg IV every 8 hours or erythromycin 500 mg IV every 6 hours until delivery is recommended.1

Centers for Disease Control and Prevention (CDC):
Revised guidelines have also been released this year from the CDC in the United States.[1]
They recommend:

all pregnant women should be screened at 35-37 weeks gestation in each pregnancy for vaginal and rectal GBS colonization and IPC should be given to all colonized women at the time of labor or rupture of membranes. (level AII evidence-strong evidence for efficacy and clinical benefit from non randomized, cohort or case-controlled studies)
the risk-based approach is no longer an acceptable alternative except in circumstances in which screening results are not available before delivery -in which case women with risk factors* should be treated(level AII evidence)
*risk factors same as # 1-3 recognized by CTFPHC (gestation < 37 wks, PROM > 18 hours or maternal fever > 38 C)
women with GBS isolated in the urine in any concentration are likely heavily colonized and should receive IPC. Vaginorectal culture at 35-37 weeks in these women is therefore not required. Lab urine specimens should be clearly labeled with pregnancy status to assist the lab in reporting results. GBS bacteriuria in pregnancy (asymptomatic or symptomatic) should be treated.
women who have previously given birth to an infant with GBS should be given IPC. (screening for colonization is not required)

The CDC Group B strep website has information for professionals and patients:
http://www.cdc.gov/groupbstrep/

Notes:

Differences between guidelines from the CDC and CTFPHC:

There are several important differences between the recommendations from these two bodies, both of which use a rigorous method of evaluating the evidence and developing the clinical practice guidelines. The differences are as follows:

the CDC report does not address the option of universal screening and selective IPC recommended by the CTFPHC.
The CDC report states that the recommendations for universal screening for all pregnant women at 35-37 weeks gestation is based on recent documentation in a large, CDC-sponsored, multi-state, retrospective cohort study of a strong protective effect of this culture-based approach relative to the risk-based strategy.[4] In the cohort of screened women in this study, 18% of all deliveries were to mothers who were colonized with GBS, but did not have risk factors. The incidence of disease among infants born to women in this cohort was 1.3 per 1000 live births. They compare this to the incidence of disease in such infants in an era before prevention (a 1985 study) which was as high as 5.1 per 1000 live births. Using this comparison, they felt the efficacy of intrapartum antibiotics in preventing early-onset disease among infants of culture-positive mothers without risk factors was almost 90%. In a personal communication with the authors of the CTFPHE report, they state that had the study by Schrag et. al. been published prior to the release of their report, it would not have changed their recommendations. The systematic review prepared for the CTFPHE included randomized controlled trials and cohort studies. They would classify this CDC study as a case-controlled study.
Also, although both studies grade the evidence as level II, the CTFPHE gives the recommendations for screening a B grade, while the CDC grades the strength of their recommendation as A.
The CDC recommends IPC for all women with a history of GBS bacteriuria, instead of screening at 35-37 weeks for vaginorectal colonization. The CTFPHC does not separately deal with the issue of GBS bacteriuria and includes it with the list of other risk factors (I believe the report appears to suggest IPC to be used only if vaginorectal colonization also found at 35-37 weeks). Studies dealing specifically with GBS bacteriuria are not listed in the references of the CTFPHC report. In a personal communication with the authors, they clarify that all women with GBS bacteriuria should be treated with IPC regardless of vaginal/rectal colonization status.
antibiotic regimens in penicillin allergic women differ slightly in the 2 reports

Recommendations of Others:

American College of Obstetricians and Gynecologists (ACOG):

A Committee Opinion released by ACOG in December 2002 states:

"The Committee on Obstetric Practice supports the new CDC recommendations that obstetric providers adopt a culture-based strategy for the prevention of early-onset GBS disease in the newborn."[5]

Notes:

In the report they note that some of the recent studies have methodologic flaws, but still constitute the best available comparison between the risk based and culture based approached.
Urine specimens should be labeled to indicated that they were obtained by pregnant women, so that laboratories will report the presence of any GBS.
GBS in the urine in concentrations of >10⁵ should be treated in both symptomatic and asymptomatic women.

The American Academy of Pediatrics in 2002 released a position statement endorsing and accepting the CDC policy on the prevention of perinatal Group B Streptococcal disease. (http://www.aap.org/policy/groupb.html)

The Society of Obstetricians and Gynecologists of Canada [6]
The September 2004 guidelines form the SOGC give the following recommendations:

Offer all women screening for group B streptococcal disease at 35 to 37 weeks' gestation with culture done from one swab first to the vagina then to the rectal area. (II-1)
Treat the following women intrapartum at time of labour or rupture of membranes with IV antibiotics:
- all women positive by GBS culture screening done at 35 to 37 weeks (II-2)
- any women with an infant previously infected with GBS (II-3)
- any women with documented GBS bacteriuria (regardless of level of colony-forming units per mL) in this pregnancy (II-2)
Treat women at less than 37 weeks' gestation with IV antibiotics unless there has been a negative GBS vaginal/rectal swab culture within 5 weeks. (II-3)
Treat women with intrapartum fever with IV antibiotics (i.e., chorioamnionitis must be treated, but broader spectrum antibiotics would be advised). (II-2)
If a woman is GBS-positive by culture screening or by history of bacteriuria, with pre-labour rupture of membranes at term, treat with GBS antibiotic prophylaxis and initiate induction of labour with IV oxytocin (II-1)
If GBS culture result is unknown and the woman has ruptured membranes at term for greater than 18 hours, treat with GBS antibiotic prophylaxis. (II-2)

National Institute for Clinical Excellence [7]
In the October 2003 document "Antenatal Care: routine care for the healthy pregnant woman", the following recommendations are given:
"Pregnant women should not be offered routine antenatal screening for group B streptococcus (GBS) because evidence of its clinical effectiveness and cost effectiveness remains uncertain" (Grade C evidence)

Conclusion:
The new guideline on the MCC will be as follows:

screen for group B strep (GBS) with vaginal-rectal culture (35-37 weeks) and offer treatment all colonized women with intrapartum IV antibiotics at the time of labour or rupture of membranes. Also offer treatment to all women with previously documented GBS bacteriuria or previous infant with GBS and women with risk factors (preterm labour < 37 weeks, PROM > 18 hours, maternal fever > 38 C) whose culture results are not available at time of delivery
also a note will be made with the guideline regarding the 12-16 week urine culture regarding alerting the laboratory to report GBS in the culture.
the guideline with be bolded as the evidence is grade B (fair evidence to include)
details about recommended IPC regimens are available on this website.
The guideline will be listed under "Investigations" for 35-37 weeks

Reviewer:
Colleen Kirkham, MD, CCFP, FCFP November 2002
Updated April 2005

4/2/2005 11:27:00 AM

1. Centers for Disease Control and Prevention. Prevention of Perinatal Group B Streptococcal Disease: revised guidelines from the CDC. MMWR, 2002. 51 (No. RR-11): p. 1-26.
2. Schuchat, A. and J.D. Wenger, Epidemiology of group B streptococcal disease. Risk factors, prevention strategies, and vaccine development. Epidemiol Rev, 1994. 16(2): p. 374-402.
3. Prevention of group B streptococcal infection in newborns: recommendation statement from the Canadian Task Force on Preventive Health Care. CMAJ, 2002. 166(7): p. 928-30.
4. Schrag, S.J., et al., A population-based comparison of strategies to prevent early-onset group B streptococcal disease in neonates. N Engl J Med, 2002. 347(4): p. 233-9.
5. ACOG Committee Opinion: number 279, December 2002. Prevention of early-onset group B streptococcal disease in newborns. Obstet Gynecol, 2002. 100(6): p. 1405-12.
6. Money, D.M. and S. Dobson, The prevention of early-onset neonatal group B streptococcal disease. Journal of Obstetrics & Gynaecology Canada: JOGC, 2004. 26(9): p. 826-32.
7. Antenatal care: routine care for the healthy pregnant woman. National Institute for Clinical Excellence. 2003 (Accessed April 5, 2004, at http://www.rcog.org.uk/resources/Public/Antenatal_Care.pdf).