Perinatal Group B Strep Testing |
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Group B streptococcus (GBS) is a leading cause of neonatal morbidity and mortality. Pre-natal screening guidelines for GBS colonization were first published by the Centers for Disease Control (CDC) in 1996, and revised in 2002 (MMWR 2002; Vol. 51, # RR-11). The revised guidelines include recommendations for universal prenatal culture screening at 35-37 weeks' gestation as well as prophylaxis regimens for women with penicillin allergy. The use of intrapartum antibiotics, based on screening culture results, has decreased the incidence of early-onset GBS disease by 70%.
The prevalence of pre-natal GBS colonization reportedly varies from 15-40%. Current literature indicates recovery of GBS from properly collected samples may be significantly improved by molecular test methods. LightCycler Real Time PCR has a sensitivity of 97.8% compared to 75.5% for culture.
Specimen collection for GBS PCR is identical to that used for culture. One or two swabs, collected from the lower vagina and rectum, should be submitted together in a Culturette transport system which is available through SLRL. Of note, is that GBS testing from ThinPrep PAP samples is not recommended by the CDC. Cervical samples are not sufficiently sensitive for detection of the organism, and antibiotic susceptibility testing is not possible from PAP specimens.
Susceptibility testing for clindamycin and erythromycin is recommended for GBS-positive, penicillin-allergic patients, and can be performed from samples submitted for PCR. The patient should be designated as 'penicillin-allergic' on the requisition and susceptibility testing should be requested.
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