Objective
The objective of the study was to estimate whether surgical lubricant used during pelvic examination alters the detection of group B Streptococcus (GBS).
Study Design
We conducted a prospective cohort study of patients undergoing GBS screening at the prenatal clinics of a New York City public hospital. Two specimens were collected from each patient, before and after a pelvic examination with Surgilube (Fougera and Co, Melville, NY), a bacteriostatic surgical lubricant. Test performance indices using GBS status pre-pelvic examination as the reference were calculated.
Results
Over 10 months, 168 patients were enrolled in the study. Twenty of 168 patients (11.9%; 95% confidence interval, 7.4–17.8%) tested GBS positive before the pelvic examination. Of the initial 20 GBS-positive patients, 10 tested GBS positive after the pelvic examination with surgical lubricant. The sensitivity of detecting GBS after the examination with surgical lubricant was 50%.
Conclusion
Because pelvic examination with surgical lubricant may decrease the detection of GBS, obstetric practitioners should collect GBS screening cultures before the use of surgical lubricant.
Group B Streptococcus (GBS) colonizes the vagina or rectum of 10-30% of pregnant women. In the 1970s, GBS emerged as the leading infectious cause of neonatal morbidity and mortality in the United States. In 2002, the American College of Obstetricians and Gynecologists and the Centers for Disease Control and Prevention (CDC) revised guidelines for intrapartum prophylaxis of GBS to include universal screening in all prenatal patients to detect GBS colonization. The 2002 CDC guidelines noted that detection of GBS increased if practitioners collected screening cultures at 35-37 weeks’ gestation, cultured both the vaginal and rectal sites, and used selective broth medium to enhance detection of GBS.
The 2002 CDC guidelines also introduced an algorithm for GBS prophylaxis for women with threatened preterm delivery. The algorithm suggests that if GBS screening culture results from the current pregnancy are unknown and the patient is at significant risk for preterm delivery, practitioners should obtain a GBS screening culture and initiate antibiotics until results are known.
Pelvic examination, sterile speculum examination for collection of cervical cultures and fetal fibronectin and/or ultrasound evaluation of cervical length are performed to assess whether a patient is at risk for preterm delivery. These examinations are usually performed with surgical lubricant to decrease patient discomfort. The active ingredient in Surgilube (Fougera and Co, Melville, NY), a commonly used surgical lubricant, is chlorhexidine gluconate.
Because this chemical has bacteriostatic properties and because the nature of placing a lubricant at the introitus may interrupt the collection of bacteria into culture medium, our objective was to study the effect of Surgilube used during pelvic examination on the detection of GBS.
Materials and Methods
Under institutional review board approval, we conducted a prospective cohort study of patients at the prenatal clinics of a New York City public hospital located in Queens, NY, affiliated with Mount Sinai School of Medicine. Patients were included in the study if they were at 35 weeks of gestation or longer and undergoing routine GBS screening culture. Patients with a history of documented GBS bacteriuria or a history of GBS sepsis in a previous neonate and patients with a contraindication to pelvic examination were excluded.
After obtaining informed consent from each study participant, we collected a GBS screening culture according to 2002 CDC guidelines by swabbing the lower vagina (vaginal introitus) and then inserting the same swab through the anal sphincter (rectum). The swab was placed in a nonnutritive transport medium (Starswab anaerobic transport system; Starplex Scientific, Inc, Ontario, Canada) and labeled “perineal” to denote pre-pelvic examination. A quarter-size amount of surgical lubricant (Surgilube) was placed on the examiner’s fingertips and pelvic examination was performed. A second GBS screening culture using the same technique and same transport medium was then collected and labeled “vaginal” to denote post–pelvic examination.
The clinical microbiology laboratory processed all GBS screening cultures using current standard-of-care procedures for the detection of GBS. The intent in labeling the pre-pelvic examination specimen “perineal” and the post-pelvic examination specimen “vaginal” was to blind the laboratory personnel, who were not aware of the significance of these terms as they related to the collection time of the specimens.
As recommended by the CDC guidelines, the swab was transferred from the nonnutritive transport medium to a selective enrichment broth (NEL-GBS medium broth; Northeast Laboratory Services, Winslow, ME). A positive result in this medium is indicated by a color change to orange between 4 and 24 hours after inoculation.
In addition, the following maternal characteristics were collected by questionnaire of the patient: age, parity, and race/ethnicity. Proportions were calculated with 95% confidence intervals. Test performance indices (sensitivity, specificity, positive predictive value, negative predictive value) were calculated using GBS screening culture status pre-pelvic examination with surgical lubricant as the reference.
Analyses were performed with Excel (Microsoft, Seattle, WA). We planned for a sample size of 182 patients using an expected incidence of GBS-positive patients of 20%, a 50% reduction in the detection of GBS, a power of 0.8, and an alpha of 0.05 with Epi Info (version 3.5.1; CDC). We terminated the study at 168 patients when the primary author left the study institution.
Results
Between March 14, 2006, and Jan. 17, 2007, 168 patients were enrolled in the study. Maternal characteristics were as follows: 86.3% were younger than 35 years of age; 47.6% were nulliparous; and 72.6% Hispanic or Latino, 20.8% Asian, 2.3% white, and 2.3% black. Twenty of 168 patients (11.9%; 95% confidence interval, 7.4–17.8%) tested GBS positive before the pelvic examination. Of the 20 GBS-positive patients, only 10 tested GBS positive after the pelvic examination with Surgilube. The sensitivity of detecting GBS after the examination with surgical lubricant was 50% ( Table ).
