What is the recommended treatment for pregnant women who test positive for group B strep (Streptococcus agalactiae)?

Treatment of Group B Streptococcus in Pregnant Women

All pregnant women should undergo universal screening for GBS colonization at 36 0/7 to 37 6/7 weeks' gestation with vaginal-rectal culture, and those who test positive must receive intravenous antibiotic prophylaxis during labor starting at least 4 hours before delivery. 1

Universal Screening Protocol

• Screen all pregnant women at 35-37 weeks' gestation using a single swab inserted first into the vagina, then through the anal sphincter into the rectum 2, 1
• This screening applies even to women planning cesarean delivery, as they remain at risk for spontaneous labor or membrane rupture before the scheduled procedure 3
• Laboratories should be informed when specimens are from pregnant women so they report GBS at concentrations ≥10,000 CFU/mL 1

Indications for Intrapartum Antibiotic Prophylaxis

You must provide IV antibiotics during labor for:

• Positive GBS screening culture at 36-37 weeks' gestation 1
• GBS bacteriuria at any concentration detected at any point during the current pregnancy—this indicates heavy colonization and requires both immediate UTI treatment AND intrapartum prophylaxis regardless of whether the UTI was treated earlier 1, 4
• Previous infant with invasive GBS disease 1
• Unknown GBS status at term with membrane rupture >18 hours 1
• Preterm labor (<37 weeks) or rupture of membranes with unknown or positive GBS status 1, 3

First-Line Antibiotic Regimen

Penicillin G is the preferred agent due to its narrow antimicrobial spectrum and universal GBS susceptibility 1:

• 5 million units IV initially
• Then 2.5 million units IV every 4 hours until delivery 1

Ampicillin is an acceptable alternative but has broader spectrum activity 4:

• 2 g IV initial dose
• Then 1 g IV every 4 hours until delivery 4

Penicillin-Allergic Patients

The choice of alternative antibiotic depends on risk stratification for anaphylaxis 1:

Low Risk for Anaphylaxis (No history of immediate hypersensitivity reactions)

• Cefazolin is the preferred alternative 1:
  • 2 g IV initial dose
  • Then 1 g IV every 8 hours until delivery 1

High Risk for Anaphylaxis (History of anaphylaxis, angioedema, urticaria, or asthma)

• Clindamycin 900 mg IV every 8 hours if the isolate is confirmed susceptible on testing 1, 4
• Vancomycin 1 g IV every 12 hours if susceptibility testing is unavailable or the isolate is resistant to clindamycin 1, 4
• Susceptibility testing for clindamycin and erythromycin is mandatory for prenatal GBS isolates from penicillin-allergic women at high risk for anaphylaxis 1

Critical Timing Requirement

• Antibiotics must be administered at least 4 hours before delivery to achieve optimal prevention of vertical GBS transmission 1
• When administered appropriately for ≥4 hours, intrapartum prophylaxis reduces early-onset GBS disease by 86-89% 1

Special Clinical Scenarios

Planned Cesarean Delivery

• Women undergoing planned cesarean delivery before labor onset with intact membranes do NOT require routine GBS prophylaxis, regardless of colonization status 1

Threatened Preterm Delivery

• Initiate GBS prophylaxis immediately while obtaining vaginal-rectal cultures 1
• Continue prophylaxis if true labor progresses
• Discontinue if labor is successfully arrested 1

Pre-labor Rupture of Membranes at Term (≥37 weeks)

• If GBS-positive: administer IV antibiotic prophylaxis AND proceed with immediate induction of labor 3
• Randomized trial data show reduced neonatal infection rates with induction versus expectant management in GBS-colonized women 3

Pre-labor Rupture of Membranes Preterm (<37 weeks)

• Administer IV GBS prophylaxis for 48 hours along with other antibiotics if indicated for latency, while awaiting spontaneous or obstetrically indicated labor 3
• For PPROM at ≥24 weeks, ampicillin 2 g IV once followed by 1 g IV every 6 hours for at least 48 hours is adequate for both latency and GBS prophylaxis 1

Intrapartum Fever and Chorioamnionitis

• Treat with broad-spectrum IV antibiotics targeting chorioamnionitis and including GBS coverage, regardless of GBS status and gestational age 3

Critical Pitfalls to Avoid

• Never treat GBS colonization with antibiotics before labor—antepartum treatment is ineffective in eliminating carriage, does not prevent neonatal disease, and promotes antibiotic resistance 1, 4
• Do not skip intrapartum prophylaxis in women with GBS bacteriuria treated earlier in pregnancy—treating the UTI does not eliminate genital tract colonization, and recolonization is typical 4
• Do not forget that GBS bacteriuria at any concentration during pregnancy mandates intrapartum prophylaxis, even if only 10,000-49,000 CFU/mL 1, 4
• Approximately 10% of persons with penicillin allergy also have immediate hypersensitivity to cephalosporins—careful allergy history is essential before using cefazolin 1