Group B Streptococcus Colonization Detection, NAA With Reflex to Susceptibilities*

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Turnaround Time: 2 - 5 days
CPT Code:

87081; 87150. If susceptibilities are performed, an additional charge will be added (87184).

Test Type: Swab of vaginal and rectal specimen


Antepartum detection of group B β-hemolytic streptococci in patients who are at high risk for anaphylactic shock due to penicillin allergy.

A positive result does not necessarily indicate the presence of viable organisms. Patients who have used systemic or topical (vaginal) antibiotic treatment in the week prior as well as patients diagnosed with placenta previa should not be tested using this assay.

In the US, group B Streptococcus (GBS) remains a leading cause of early-onset neonatal sepsis. The most common mode of acquisition by the neonate is exposure to the maternal genital flora in utero through ruptured membranes or by contamination during passage through the birth canal.

Infection is manifested in two major forms, early-onset septicemic infection manifest in the first few days of life and late-onset meningitis that occurs during the first few months of life. The Centers for Disease Control and Prevention (CDC) and the American Congress of Obstetricians and Gynecologists (ACOG) practice guidelines recommend universal antepartum screening at 35 to 37 weeks of gestation. These guidelines specify co-collection of a vaginal and rectal swab specimen to maximize sensitivity of GBS detection. Per the CDC and ACOG, swabbing both the lower vagina and rectum substantially increases the yield of detection compared with sampling the vagina alone. Rates of maternal colonization have not changed, but universal antepartum screening along with the use of intrapartum antibiotic prophylaxis has resulted in a decrease of early-onset GBS disease. In November 2010, the CDC published revised guidelines recommending that, in addition to culture, antepartum vaginal/rectal specimens could be tested using a nucleic acid amplification (NAA) test following incubation in a selective enrichment broth medium to enhance the detection of GBS.

Susceptibility testing is not routinely performed, as this organism is universally susceptible to penicillin, and surveillance for resistance is not recommended. The CDC and the ACOG recommend reflex susceptibility testing to clindamycin and erythromycin (D-zone test to detect inducible clindamycin resistance) for group B Streptococcus only for those patients at high risk for anaphylactic shock due to penicillin allergy.

For those patients without likely evidence of severe anaphylaxis, the CDC and ACOG recommend the use of cefazolin as the agent of choice for intrapartum chemoprophylaxis without the need for susceptibility testing. For those patients with GBS that is resistant to clindamycin, treatment with vancomycin is recommended without the need for additional susceptibility testing. Even though it is tested together with clindamycin in the D-zone test, erythromycin is no longer an acceptable alternative for intrapartum GBS prophylaxis for penicillin-allergic women at high risk for anaphylaxis, and susceptibility results for this agent will not be reported.

American College of Obstetricians and Gynecologists Committee on Obstetric Practice. ACOG Committee Opinion N° 485: Prevention of early-onset group B streptococcal disease in newborns. Obstet Gynecol. 2011 Apr; 117(4):1019-1027. PubMed 21422882

Haberland CA, Benitz WE, Sanders GD, et al. Perinatal screening for group B streptococci: Cost-benefit analysis of rapid polymerase chain reaction. Pediatrics. 2002 Sep; 110(3):471-480. PubMed 12205247

Park JS, Cho DH, Yang JH, et al. Usefulness of a rapid real-time PCR assay in prenatal screening for group B Streptococcus colonization. Ann Lab Med. 2013 Jan; 33(1):39-44. PubMed 23301221

Picard FJ, Bergeron MG. Laboratory detection of group B Streptococcus for prevention of perinatal disease. Eur J Clin Microbiol Infect Dis. 2004 Sep; 23(9): 665-671. PubMed 15258832

Verani JR, McGee L, Schrag SJ; Division of Bacterial Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention (CDC). Prevention of perinatal group B streptococcal disease--revised guidelines from CDC, 2010.MMWR Recomm Rep. 2010 Nov 19; 59(RR-10):1-36. PubMed 21088663

Collection Details:

Collection Instructions:

Collection of both a vaginal and rectal swab specimen is strongly recommended. Swab the lower vagina (vaginal introitus), followed by the rectum (ie, insert swab through the anal sphincter) using the same swab. Move swab from side to side, or rotate the swab at the collection site, allowing several seconds for absorption of organisms by the swab. Cervical, perianal, perirectal or perineal specimens are not acceptable, and a speculum should not be used for culture collection.

Specimen is stable for 24 hours at room temperature. If arrival at lab will extend beyond 24 hours, then refrigerate.