ACOG updates guidance on preventing early-onset GBS disease
American College of Obstetricians and Gynecologists—Committee on Obstetric Practice. ACOG committee opinion no. 782: prevention of early-onset group B streptococcal disease in newborns. Obstet Gynecol. 2019;134:e19-e40.
Group B streptococcus (GBS) is the leading cause of newborn infection and is associated with maternal infections as well as preterm labor and stillbirth. Early-onset GBS disease occurs within 7 days of birth and is linked to vertical transmission via maternal colonization of the genitourinary or gastrointestinal tract and fetal/neonatal aspiration at birth.
Preventing early-onset GBS disease with maternal screening and intrapartum prophylaxis according to the Centers for Disease Control and Prevention (CDC) guidelines has reduced early-onset disease by 80% since the 1990s. By contrast, late-onset GBS infection, which occurs 7 days to 3 months after birth, usually is associated with horizontal maternal transmission or hospital or community infections, and it is not prevented by intrapartum treatment.
In 2018, the CDC transferred responsibility for GBS prophylaxis guidelines to ACOG and the American Academy of Pediatrics (AAP). In July 2019, ACOG released its Committee Opinion on preventing early-onset GBS disease in newborns.8 This guidance replaces and updates the previous guidelines, with 3 notable changes.
The screening timing has changed
In the CDC's 2010 guidelines, GBS screening was recommended to start at 35 weeks' gestation. The new guidelines recommend universal vaginal-rectal screening at 36 to 37 6/7 weeks' gestation. The new timing of culture will shift the expected 5-week window in which GBS cultures are considered valid up to at least 41 weeks' gestation. The rationale for this change is that any GBS-unknown patient who previously would have been cultured under 37 weeks' would be an automatic candidate for empiric therapy and the lower rate of birth in the 35th versus the 41st week of gestation.
Identifying candidates for intrapartum treatment
The usual indications for intrapartum antibiotic prophylaxis include a GBS-positive culture at 36 weeks or beyond, GBS bacteriuria at any point in pregnancy, a prior GBS-affected child, or unknown GBS status with any of the following: < 37 weeks, rupture of membranes ≥ 18 hours or temperature ≥ 100.4°F (38°C), and a positive rapid GBS culture in labor. In addition, antibiotics now should be considered for patients at term with unknown GBS status but with a history of GBS colonization in a prior pregnancy.
This represents a major practice change for women at ≥ 37 weeks with unknown GBS status and no other traditional risk factors. The rationale for this recommendation is that women who have been positive for GBS in a prior pregnancy have a 50% chance of being colonized in the current pregnancy, and their newborns are therefore at higher risk for early-onset GBS disease.
Managing patients with penicillin allergy
Intravenous penicillin (or ampicillin) remains the antibiotic of choice for intrapartum prophylaxis against GBS due to its efficacy and specific, narrow coverage of gram-positive organisms. The updated recommendations emphasize that it is important to carefully evaluate patients with reported penicillin allergies for several reasons: determining risk of anaphylaxis and clindamycin susceptibility testing in GBS evaluations are often overlooked by obstetric providers, the need for antibiotic stewardship to reduce the development of antibiotic resistance, and clarification of allergy status for future health care needs.
Three recommendations are made:
- Laboratory requisitions for cultures should specifically note a penicillin allergy so that clindamycin susceptibility testing can be performed.
- Penicillin allergy skin testing should be considered for patients at unknown or low risk for anaphylaxis, as it is considered safe in pregnancy and most patients (80%-90%) who report a penicillin allergy are actually penicillin tolerant.
- For patients at high risk for anaphylaxis to penicillin, the recommended vancomycin dosing has been changed from 1 g IV every 12 hours to 20 mg/kg IV every 8 hours (maximum single dose, 2 g). Renal function should be assessed prior to dosing. This weight- and renal function-based dosing increased neonatal therapeutic levels in several studies of different doses.
WHAT THIS EVIDENCE MEANS FOR PRACTICE
ACOG's key recommendations for preventing early-onset GBS disease in newborns include:
- Universal vaginal-rectal screening for GBS should be performed at 36 to 37 6/7 weeks' gestation.
- Intrapartum antibiotic prophylaxis should be considered for low-risk patients at term with unknown GBS status and a history of GBS colonization in a prior pregnancy.
- Patients with a reported penicillin allergy require careful evaluation of the nature of their allergy, including consideration of skin testing and GBS susceptibility evaluation in order to promote the best practices for antibiotic use.
- For GBS-positive patients at high risk for penicillin anaphylaxis, vancomycin 20 mg/kg IV every 8 hours (maximum single dose, 2 g) is recommended.
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