From Medscape today...


Neonatal Group B Streptococcal Disease Prevention

Gilles R. G. Monif, MD

In 1996, guidelines for the prevention of neonatal group B streptococcal
disease were issued by the American College of Obstetricians and
Gynecologists, the American Academy of Pediatrics, and the CDC. Two
approaches were advocated to identify candidates for intrapartum antibiotic
prophylaxis. The first of these was a maternal risk-based approach in which
intrapartum antibiotics would be administered to pregnant women with preterm
deliveries, prolonged rupture of the fetal membranes, intrapartum fever,
prior neonatal disease caused by group B Streptococcus (GBS), or GBS
bacteriuria. The second was a bacteriologic screening approach that entailed
obtaining cultures from pregnant women to check for vaginal and rectal GBS
carriage between 35 and 37 weeks of gestation and offering intrapartum
chemoprophylaxis to those identified as being colonized. The latter approach
was subsequently modified to include gravidas with GBS bacteriuria and women
who had given birth to a GBS-infected neonate. Both approaches were
recommended as equally acceptable.

Schrag and colleagues (N Engl J Med. 2002;347:233-239) reported on a
multistate retrospective cohort study involving 5144 births in which they
compared the 2 officially recommended strategies. According to their
univariate statistical analysis, prenatal screening for GBS was associated
with a lower risk of early-onset neonatal disease than was the risk-based
approach (relative risk, 0.48; 95% confidence interval, 0.38 to 0.61).
Intrapartum maternal fever and previously having a neonate with GBS disease
had the highest correlation with the risk of early-onset disease. Gravidas
with GBS bacteriuria did not exhibit an increased risk; however, the
significance of that finding was limited by the fact that the majority of
these women were identified and treated within the bacteriologically
screened group and, overall, 82% of women with GBS bacteriuria received
intrapartum antibiotics. Using risk factors without significant screening
for asymptomatic bacteriuria makes it more likely than not that the majority
of gravidas with untreated GBS asymptomatic bacteriuria resided in the
maternal risk-factor group.

A key observation was the finding that in the screening group, 18% of all
gravidas did not present with an identified maternal risk factor. The
incidence of neonates with GBS disease born to mothers without risk factors
was 1.3 per 1000 live births. The efficacy of intrapartum antibiotics in
preventing early-onset disease among newborns born to culture-positive
pregnant women without risk factors was close to 90%. The authors found that
the screening approach for the prevention of neonatal GBS bacteriuria was
more than 50% more effective than the risk-based approach. They therefore
called for reconsideration of recommendations that endorse both strategies
as equivalent. While well done, this study has inherent problems
characteristic of retrospective studies using multiple sites. Which approach
should be advocated may not be the key issue. Both approaches have
significantly reduced GBS neonatal disease but have not eliminated it. The
tight focus on the obstetric/perinatal aspects of disease has precluded
development of a significant pediatric preventive intervention.

Before the 1996 guidelines, universal administration of penicillin to all
neonates profoundly altered the incidence of ensuing neonatal GBS disease.
Unlike in pregnant women, anaphylaxis has not been described in a newborn
(Obstet Gynecol. 1996;87:692-698). The drug per se is relatively
inexpensive. Wendel and colleagues (Am J Obstet Gynecol. 2002;186:618-626)
have calculated that almost 1400 neonates could receive single-dose
prophylaxis with 50,000 units of penicillin G for the cost of a single
successful treatment of 1 GBS-affected baby.

Wendel and coauthors used an approach combining both risk factors and
culture surveillance with universal neonatal penicillin administration to
achieve excellent results in a high-risk population. They demonstrated that
a protocol of intrapartum ampicillin given to pregnant women at risk for
bearing neonates with GBS sepsis combined with routine penicillin G
prophylaxis given to all other neonates dramatically reduced the incidence
of GBS disease and did so without increasing the rate of sepsis from other
bacteria.

Such a strategy is the missing prevention approach in the CDC's comparative
study. Without a pediatric component, no obstetric prevention program will
meet society's mandate with respect to GBS disease prevention.

Infect Med 20(8):370,373, 2003. (c) 2003 Cliggott Publishing, Division of
SCP Communications

---------
Katherine Shealy



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