Benefits of Group B Strep Prophylaxis
Abstract & Commentary
Source: Locksmith GJ, et al. Am J Obstet Gynecol 1999;180:416-422.
To determine the efficacy of Group B Streptococcal (GBS) prevention strategies to reduce the rates of maternal and neonatal infection, Locksmith and colleagues compared outcomes resulting from the use of three different protocols between August 1, 1991, and April 30, 1998. During the first two years of the study, GBS cultures were obtained only when patients were admitted with preterm premature rupture of the membranes (PPROM) or preterm labor, and intrapartum treatment was given when the patient had a recognized risk factor for early onset of GBS infection and a positive culture result. During the next three years, the American College of Obstetricians and Gynecologists (ACOG) protocol was adopted with intrapartum antibiotics offered to women whose colonization status was unknown but who had risk factors including delivery before 37 weeks gestation, PPROM, membrane rupture greater than 18 hours, maternal fever indicating chorioamnionitis, and a previous infant with GBS infection. In the last two years of the study, the Centers for Disease Control and Prevention (CDC) protocol was followed, with cultures performed on all patients between 35-37 weeks gestation and antibiotics administered to all of those with a positive culture. If the colonization status was not known, antibiotics were given on the basis of risk factors. In the past, patients with an infant affected by GBS disease or GBS bacteriuria were uniformly treated. During the first year of the study, patients with PPROM who were managed expectantly received intravenous ampicillin followed by oral amoxicillin until culture results were known. Thereafter, they were given intravenous ticarcillin and clavulanic acid followed by amoxicillin.
The universal screening protocol recommended by the CDC significantly reduced the rates of clinical chorioamnionitis and postpartum endometritis when compared to the selective screening and ACOG protocols. While there was a trend toward a reduced rate of neonatal infection with the ACOG and CDC protocols, this difference was not statistically significant. The ACOG protocol did significantly lower the rate of neonatal GBS infection in infants delivered to mothers with risk factors (selective screening 7.20/1000, ACOG protocol 2.15/1000, CDC protocol 3.13/1000). Most of the neonatal GBS infections in patients managed with these protocols occurred as a result of protocol failures; that is, the patient was not a candidate for prophylaxis or was given antibiotics but an infection still developed.
Locksmith et al conclude that universal screening for GBS infection prevention significantly reduced the rates of clinical chorioamnionitis and endometritis and may decrease neonatal GBS infection as well. However, the size of the study population was not sufficient to demonstrate this difference.
COMMENT BY STEVEN G. GABBE, MD
GBS infection is an important cause of neonatal morbidity and mortality. The rate of neonatal GBS infection in the United States each year is nearly 2/1000 or approximately 10,000 cases of neonatal GBS septicemia. The mortality associated with GBS infection is 5% in term infants and rises to 25% in preterm infants. Intrapartum chemoprophylaxis with intravenous penicillin G (5 million U initially and then 2.5 million U every 4 hours until delivery) or intravenous ampicillin (2 g loading dose followed by 1 g every 4 hours until delivery) significantly reduces neonatal colonization and bacteremia. In this retrospective study by Locksmith et al, the experience with three different protocols used over seven years is presented. It has been estimated that an investigation of 110,000 women would be required to demonstrate a significant difference in neonatal outcome. In the present investigation, a little more than 20,000 women were studied. While significant differences in the neonatal GBS attack rates were not seen, the ACOG and CDC protocols did demonstrate greater efficacy, particularly when patients with risk factors were managed with the ACOG protocol. GBS is also an important cause of chorioamnionitis and endometritis, and Locksmith et al have shown a significant reduction in the rates of these complications with universal screening.
While this study does have some problems—patient management is likely to change over seven years—different culture techniques were used during the study, and the overall rate of positive cultures was not reported. This investigation provides a "real life" overview of the application of the recommended protocols for the prevention of GBS infection. However, despite the best efforts of the clinicians, there were protocol failures. Which strategy should be adopted? It would appear reasonable for the clinician to choose either the CDC protocol based upon cultures at 35-37 weeks or the ACOG protocol based on clinical risk factors.
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