Intrapartum Vancomycin for Group B Streptococcus (GBS) Prophylaxis

Overview

While it is clear that intrapartum antibiotics reduce neonatal GBS infection rates, the mechanism by which these drugs prevent neonatal GBS is not well established. One postulated theory is antibiotics work to reduce bacterial load in the birth canal; thus decreasing fetal exposure during labor and delivery. To our knowledge, the relationship between vancomycin and vaginal GBS colony counts has never been studied. In this prospective cohort study, our objective is to determine the relationship between intrapartum IV vancomycin and vaginal GBS colony counts.

Charts of patients presenting for induction of labor will be reviewed for potential eligibility. After provider permission, eligible patients will be approached for screening who are presenting for induction with documented GBS positivity and plan for vancomycin for intrapartum antibiotic prophylaxis. Patients presenting to the emergency room for labor evaluation/labor evaluation/pre-term labor evaluation, may be pre-screened for potential eligibility. Patients subsequently admitted in labor/preterm labor or with rupture of membranes with documented GBS positivity and plan for vancomycin for intrapartum antibiotic prophylaxis will be approached for screening. Additionally pharmacy will alert study staff when a patient is admitted to the labor floor or antenatal care unit and vancomycin has been ordered for antibiotic prophylaxis. These patients will then be approached for screening Data collection: Demographic information such as age, race, date of initial GBS culture and time of rupture of membranes will be abstracted from enrolled patients' charts. Intrapartum vaginal cultures will be collected with a vaginal swab from the distal vagina by trained obstetrics and gynecology residents, attendings, nurses, nurse midwives and nurse practitioners prior to the initiation of antibiotics and at two hour intervals until delivery or after eight hours has elapsed. Swabs will be transported to the lab. Colony counts will be determined via serial dilution. Specimens will be diluted in sterile saline and inoculated onto Columbia Agar containing 5% sheep blood, colistin (10 mg), and nalidixic acid (10 mg/L). After incubation for 48 hours at 35 C in ambient air, the number of colonies on the dilution plates will be visually counted and multiplied by the appropriate dilution factor for that particular plate.