BACKGROUND: Group B streptococcus (GBS) sepsis affects approximately 2 of every 1000 newborns. In an effort to decrease the incidence of neonatal GBS infection, the Centers for Disease Control and Prevention have established guidelines for screening and treatment during pregnancy. One strategy includes obtaining both vaginal and anorectal GBS cultures, then treating patients whose cultures are positive. Many of our patients are reluctant to undergo anorectal cultures. We conducted a study to determine whether performing cultures of both the vagina and anorectum would change patient management.
METHODS: We obtained vaginal and anorectal GBS cultures from 222 consecutive patients at 35 to 37 weeks’ gestation.
RESULTS: Fifty-four patients (24.3%) had positive GBS cultures. Of those women, 10 (18.5%) had negative vaginal but positive rectal cultures. Thus, nearly one fifth of the patients with GBS colonization would not have received intrapartum antibiotics if only vaginal cultures had been performed.
CONCLUSIONS: Health care providers caring for pregnant patients should consider obtaining both vaginal and anorectal cultures when screening for Group B streptococcus.
Approximately 7600 neonates develop Group B streptococcus (GBS) sepsis each year in the United States.1 To decrease its incidence, the Centers for Disease Control (CDC) and Prevention, working with the American College of Obstetricians and Gynecologists (ACOG), the American Academy of Pediatrics, and other organizations developed guidelines for the prevention of GBS sepsis.2 The CDC and ACOG have recommended 2 possible approaches.2,3 One is to treat patients on the basis of clinical risk factors. The other is to screen all pregnant women for GBS carrier status by obtaining vaginal and anorectal cultures at 35 to 37 weeks’ gestation and provide intrapartum antibiotics to those patients with positive cultures. In our practice we have adopted the screening strategy. However, we have found that some patients are reluctant to undergo anorectal cultures.
To determine whether the results obtained from anorectal cultures would change patient treatment, we obtained vaginal and anorectal GBS cultures from every pregnant patient, according to the CDC guidelines, and evaluated the data from the culture results.
Methods
We offered routine GBS screening cultures of the vagina and anorectum to all pregnant patients at the faculty practice of the Florida Hospital Family Practice Residency Program from April 1998 through April 1999. A total of 223 women from a predominantly middle-income background who were at 35 to 37 weeks’ gestation gave informed consent for inclusion in the study. One patient refused an anorectal culture, leaving 222 patients for analysis.
Culture specimens were prepared as follows: Vaginal swabs were separated into 2 specimens. The first was immediately plated onto sheep blood agar, while the second was inoculated into Lim broth, incubated for 18 to 24 hours, and subcultured onto sheep blood agar. After 48 hours both plates were read. If either the blood agar plate or the Lim broth preparation grew GBS, the results were reported as positive. Anorectal cultures were prepared similarly, with the exception that the sheep blood agar was prepared with an inhibitory preparation of colistin/nalidixic acid agar (CNA) to preferentially isolate gram-positive organisms.
Results
Of the 222 patients evaluated, cultures in 1 or more sites were positive for GBS in 54 (24.3%) patients. Of those women, 37 (68.5%) had positive vaginal and anorectal cultures, 7 (13.0%) had only positive vaginal cultures, and 10 (18.5%) had only positive anorectal cultures. Results are listed in the Table 1; none of the specimens were inadequate for evaluation.
Discussion
Several organizations, including the CDC,2 ACOG,3 and the American Academy of Pediatrics4 have suggested that health care providers caring for pregnant women should implement a strategy for GBS prevention. We use the screening approach and obtain vaginal and anorectal cultures from women at 35 to 37 weeks’ gestation. However, some of our patients have expressed reservations about undergoing anorectal cultures. Other investigators have noted similar concerns and have suggested that patients may prefer self-collection of GBS cultures.5,6 We conducted this study to determine if eliminating anorectal cultures would alter the intrapartum management of our patients.
Our study revealed that 24.3% of our pregnant patients were colonized with GBS in the vagina, anorectum, or both. These findings are similar to other published GBS colonization rates during pregnancy of between 10% and 30%.7,8 Anorectal colonization was more common than vaginal colonization in our patient population. Others have noted similar findings and have suggested that the genital tract may be contaminated by GBS arising primarily from the anorectum.9,10
Data are lacking on whether there is a differential neonatal sepsis rate from GBS colonization of the vagina in contrast with the anorectum. Since GBS sepsis occurs in approximately 2 of every 1000 newborns, it would take a large study to compare sepsis rates from different sites. This type of study would require withholding antibiotics from patients with GBS colonization to compare neonatal sepsis rates from patients with vaginal as opposed to anorectal colonization. Such a study would be unethical. Therefore, we suggest using current CDC guidelines and treating all pregnant patients with a positive GBS culture from the vagina, rectum, or urine with intrapartum antibiotics. Since preparing the specimens in the laboratory using appropriate incubation and culture technique affects the sensitivity and specificity of the results,11 we suggest contacting local laboratory directors to ensure that each lab is using the current CDC guidelines.