What is the treatment for a patient with 10,000-49,000 Colony-Forming Units per milliliter (CFU/mL) of Group B Streptococcus isolated on urine culture?

Treatment of 10,000-49,000 CFU/mL Group B Streptococcus in Urine Culture

This colony count (10,000-49,000 CFU/mL) falls below the CDC reporting threshold of ≥10⁴ CFU/mL (≥10,000 CFU/mL), but since 10,000 CFU/mL meets the threshold, treatment decisions depend critically on pregnancy status: pregnant women require immediate treatment and intrapartum prophylaxis at any GBS concentration, while non-pregnant adults should only be treated if symptomatic or have underlying urinary tract abnormalities. 1, 2, 3

For Pregnant Women

All pregnant women with GBS isolated from urine at any concentration during pregnancy must receive treatment and intrapartum antibiotic prophylaxis during labor, regardless of the colony count. 3

Immediate Management

• GBS bacteriuria in pregnancy indicates heavy colonization and significantly increases the risk of early-onset neonatal GBS disease, which supersedes typical UTI treatment thresholds. 3
• Treat symptomatic GBS UTI immediately according to standard UTI protocols, but intrapartum prophylaxis is still required during labor regardless of prior treatment. 3
• Prenatal culture-based screening at 35-37 weeks is not necessary for these women since they already qualify for prophylaxis based on the positive urine culture. 3

Antibiotic Selection

• First-line treatment: Penicillin G or ampicillin as an acceptable alternative. 1, 3, 4
• For penicillin-allergic women without high risk for anaphylaxis (no history of anaphylaxis, angioedema, respiratory distress, or urticaria): use cefazolin. 1
• For penicillin-allergic women at high risk for anaphylaxis: perform antimicrobial susceptibility testing for clindamycin and erythromycin, as approximately 20% of GBS isolates are resistant to clindamycin. 1, 3, 5

Critical Caveat

• Clinicians must inform laboratories when submitted urine specimens are from pregnant women to ensure proper testing and reporting, as GBS at any concentration is clinically significant in this population. 1, 3

For Non-Pregnant Adults

Non-pregnant adults with GBS bacteriuria at this concentration should only be treated if they are symptomatic or have underlying urinary tract abnormalities. 3, 6

When to Treat

• Symptomatic patients with dysuria, frequency, urgency, flank pain, or fever require treatment. 6
• Asymptomatic patients should undergo evaluation for underlying urinary tract abnormalities, as 60% of non-pregnant adults with GBS bacteriuria have structural urinary tract problems. 6
• Common underlying conditions include chronic renal failure (27% of cases), diabetes mellitus, and malignant neoplasms. 7, 6

When NOT to Treat

• Asymptomatic bacteriuria in non-pregnant adults without urinary tract abnormalities does not require treatment, as this increases antibiotic resistance risk and adverse effects (including Clostridioides difficile diarrhea) without clinical benefit. 8, 9
• Screening and treatment of asymptomatic bacteriuria is not recommended in older patients, diabetic patients, or patients with indwelling urethral catheters. 9

Antibiotic Selection for Symptomatic Non-Pregnant Adults

• High-dose penicillin G is recommended for serious GBS infections due to somewhat higher minimal inhibitory concentrations compared to other streptococci. 7
• All GBS isolates are sensitive to penicillin, ampicillin, cephalosporins, and clindamycin (if susceptibility confirmed), but resistant to gentamicin. 6
• Surgical management may be required in addition to antibiotics for soft-tissue or bone infections. 7

Laboratory Reporting Standards

• Laboratories should report GBS in urine culture specimens when present at concentrations of ≥10⁴ CFU/mL in pure culture or mixed with a second microorganism. 1, 2
• The colony count of 10,000-49,000 CFU/mL meets the threshold for reporting (≥10,000 CFU/mL = ≥10⁴ CFU/mL). 1

Common Pitfall to Avoid

The most critical error is failing to recognize pregnancy status: treating a pregnant woman's GBS bacteriuria as if she were non-pregnant (waiting for symptoms) can result in preventable neonatal sepsis and death, while overtreating asymptomatic non-pregnant adults contributes to antibiotic resistance without benefit. 3, 9