Beta Strep (Group B) Antigen

Test ID: 

70512

CPT code:

87801

Synonyms:

Culture, Genital, Group B β-Hemolytic Streptococcus

Genital β-Hemolytic Culture, Group B

Group B β-Hemolytic Strep Culture, Vaginal or Rectal

β-Hemolytic Streptococcus Culture, Group B Only, Any Source

Clinical Use:

Isolate and identify group B β-streptococci

Test Information:

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.

Specimen Type:

Swab of vaginal and rectal specimen

Requested Volume: 

Single or double bacterial swab in Amies agar gel transport or equivalent

Minimum Volume: 

Single or double bacterial swab in Amies agar gel transport or equivalent

Container Type: 

bacterial swab in Amies agar gel transport or equivalent

Collection:

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.

Storage Instructions:

Maintain specimen at room temperature.

Rejection Criteria

Inappropriate specimen transport; use of ESwab™; inappropriate transport conditions; improper labeling; specimen received after prolonged delay (more than 48 hours); cervical/endocervical, perianal, perirectal or perineal specimen or any source other than vagina and rectum

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