Management of Group B Streptococcus Throat Culture in Pregnancy
GBS isolated from a throat culture in a pregnant patient does not require treatment and does not indicate the need for intrapartum antibiotic prophylaxis. 1
Why Throat Cultures Are Not Relevant for GBS Management
The CDC guidelines specify that only vaginal-rectal GBS colonization matters for pregnancy management, as vertical transmission to the newborn occurs during labor through passage through the birth canal, not through respiratory or pharyngeal colonization 1
Throat or pharyngeal GBS colonization has no established correlation with genital tract colonization and does not predict risk of early-onset neonatal GBS disease 1
The standard screening site is vaginal-rectal swabs at 36 0/7 to 37 6/7 weeks' gestation, not throat cultures, because this is where colonization relevant to neonatal transmission occurs 2, 3
What Actually Requires Treatment in Pregnancy
The only GBS findings that mandate action during pregnancy are:
GBS bacteriuria at any concentration during any trimester requires immediate treatment of the UTI plus mandatory intrapartum IV antibiotic prophylaxis during labor 4, 3
Positive vaginal-rectal culture at 36 0/7 to 37 6/7 weeks' gestation requires intrapartum antibiotic prophylaxis during labor 1, 2
History of previous infant with invasive GBS disease requires intrapartum prophylaxis without need for screening 1
Correct Screening Protocol
Perform vaginal-rectal swab (not throat culture) at 36 0/7 to 37 6/7 weeks' gestation using a single swab inserted into the lower vagina first, then through the anal sphincter into the rectum 1, 2
Do not collect specimens by speculum examination as lower vaginal cultures (not cervical) are required 1
Specimens should be placed in non-nutritive transport medium and inoculated into selective broth medium with overnight incubation 1
Critical Pitfall to Avoid
Never treat asymptomatic GBS colonization (vaginal-rectal or throat) with oral or IV antibiotics before labor, as this is completely ineffective at eliminating carriage, does not prevent neonatal disease, and promotes antibiotic resistance 1, 4
Intrapartum IV prophylaxis during active labor is the only effective intervention for preventing early-onset neonatal GBS disease, reducing risk by 78% when administered ≥4 hours before delivery 4, 2
If This Patient Needs GBS Screening
Obtain proper vaginal-rectal culture at 36 0/7 to 37 6/7 weeks' gestation if not already performed 2, 3
If positive, administer penicillin G 5 million units IV initially, then 2.5 million units IV every 4 hours during labor until delivery 1, 4
Alternative for penicillin allergy without high-risk features: cefazolin 2 g IV initially, then 1 g IV every 8 hours 1, 4