What are the causes and treatment options for Group B Streptococcus (GBS) in a 25-year-old female?

Group B Streptococcus in a 25-Year-Old Female: Causes and Treatment

Causes and Colonization

Group B Streptococcus (GBS) colonization in a 25-year-old woman originates from the gastrointestinal tract, which serves as the natural reservoir, with subsequent spread to the vaginal and rectal areas. 1, 2

• Approximately 10-30% of women of reproductive age are colonized with GBS in the vagina or rectum 1
• Colonization becomes more common in late adolescence and can be transient, chronic, or intermittent 1
• The gastrointestinal tract is the primary source, with secondary vaginal colonization occurring through anatomic proximity 1, 2

Clinical Manifestations in Non-Pregnant Women

GBS can cause several types of infections in a 25-year-old woman:

• Urinary tract infections: GBS accounts for 1.79-8.92% of positive urine cultures in women, manifesting as cystitis, pyelonephitis, or urosepsis 2
• Asymptomatic bacteriuria: Presence of GBS in urine without symptoms, which requires different management than symptomatic infection 3, 2
• Risk factors for GBS UTI include diabetes mellitus and underlying urinary tract abnormalities 2

Treatment Approach: Critical Distinction Based on Pregnancy Status

If NOT Pregnant (Symptomatic UTI)

For a non-pregnant 25-year-old with symptomatic GBS UTI, treat with ampicillin 500 mg orally every 8 hours for 3-7 days, or amoxicillin 500 mg orally every 8 hours as an equally effective alternative. 4

• Obtain urine culture before initiating therapy to confirm diagnosis (significant bacteriuria defined as ≥50,000 CFUs/mL) 4
• Do NOT treat asymptomatic bacteriuria in non-pregnant patients - this represents colonization, not infection, and treatment leads to unnecessary antibiotic resistance without clinical benefit 3, 2
• For penicillin-allergic patients, use cephalexin orally or cefazolin 2 g IV initial dose, then 1 g IV every 8 hours 4
• For complicated UTIs or severe infections, escalate to ampicillin 18-30 g/day IV in divided doses 4

If Pregnant

Any concentration of GBS bacteriuria during pregnancy mandates immediate treatment of the acute UTI PLUS intrapartum antibiotic prophylaxis during labor, regardless of symptoms or colony count. 4, 2

• Treat the acute UTI at time of diagnosis according to standard protocols 4
• Provide intrapartum prophylaxis during labor with penicillin G 5 million units IV initially, then 2.5-3.0 million units IV every 4 hours until delivery 4
• GBS bacteriuria during pregnancy serves as a marker for heavy genital tract colonization and increased risk of neonatal disease 2
• Women with documented GBS bacteriuria do not require vaginal-rectal screening at 35-37 weeks 2

Duration of Therapy

• Uncomplicated UTI: 3-7 days 4
• Complicated UTI: 5-7 days 4
• Severe infections or bacteremia: 10-14 days 4

Critical Pitfalls to Avoid

The most dangerous error is treating asymptomatic GBS bacteriuria in non-pregnant women or failing to provide intrapartum prophylaxis in pregnant women with any GBS bacteriuria. 4, 3

• Underdosing or premature discontinuation leads to treatment failure and recurrence 4
• Do NOT use clindamycin without susceptibility testing due to high resistance rates 4
• Distinguish true infection (symptoms + abnormal urinalysis) from colonization (positive culture without symptoms) 4, 3
• In pregnancy, failing to provide intrapartum prophylaxis increases neonatal mortality risk 4

Antibiotic Selection Algorithm

For penicillin-allergic patients:

• Low risk of anaphylaxis: Cefazolin 5
• High risk of anaphylaxis: Clindamycin or erythromycin (with susceptibility testing) 5
• Resistance to clindamycin/erythromycin or unknown susceptibility: Vancomycin 5