What is the treatment for a non-pregnant patient with a urine culture showing 10,000-50,000 colonies of Staphylococcus (coagulase-negative staphylococci) and Streptococcus agalactiae (Group B streptococcus)?

Treatment for Non-Pregnant Patient with Urine Culture Showing Staphylococcus Coagulase-Negative and Group B Streptococcus

For a non-pregnant patient with a urine culture showing 10,000-50,000 colonies of coagulase-negative Staphylococcus and Streptococcus agalactiae (Group B streptococcus), penicillin G is the first-line treatment if the patient is symptomatic and the culture represents a true urinary tract infection. 1

Determining Clinical Significance

Before initiating treatment, it's important to determine whether this represents true bacteriuria or contamination:

• Colony count of 10,000-50,000 CFU/mL falls in a gray zone that may represent either true infection or contamination
• Research shows that even with ≥100,000 CFU/mL of GBS in voided urine, one-third of patients had contamination rather than true bacteriuria 2
• Clinical assessment is crucial:
  • Presence of urinary symptoms (dysuria, frequency, urgency)
  • Fever (though less common with GBS than with E. coli infections) 2
  • Presence of urinary tract abnormalities (common in patients with GBS UTI) 3

First-Line Treatment Options

If clinical assessment suggests true UTI:

1. Penicillin G: First-line therapy for GBS infections 1

   • Dosing: 5 million units IV initial dose, followed by 2.5-3.0 million units IV every 4 hours

2. Ampicillin: Acceptable alternative to penicillin G 1

   • Dosing: 2 g IV initial dose, then 1 g IV every 4 hours

Alternative Treatment Options for Penicillin-Allergic Patients

For patients with penicillin allergy:

1. Clindamycin: 600-900 mg IV every 8 hours (if isolate is susceptible) 1

2. Vancomycin: 15-20 mg/kg IV every 8-12 hours (for resistant strains or when susceptibility is unknown) 1

Special Considerations

• Mixed infection management: Since both coagulase-negative Staphylococcus and GBS are present, consider broader coverage if clinically indicated:

  • Ampicillin-sulbactam plus clindamycin
  • Or single agents like imipenem/cilastatin, meropenem, or ertapenem 1

• Susceptibility testing: Important to perform susceptibility testing before treatment, as some strains may be resistant 4

• Duration of therapy: Continue antibiotics until clinical improvement is evident and the patient has been afebrile for 48-72 hours 1

Risk Factors to Consider

• GBS infections are increasingly recognized in non-pregnant adults, particularly in those with:
  • Age ≥60 years 5
  • Diabetes mellitus 6
  • Urinary tract abnormalities (present in 60% of cases) 3
  • Chronic renal failure (27% of cases) 3
  • Liver disease (more common in males) 5
  • Malignancy (more common in females) 5

Monitoring and Follow-up

• Evaluate for signs of invasive disease, as GBS can cause serious complications including bacteremia, meningitis, and endocarditis 6, 7
• Document clearance of infection with follow-up urine cultures
• Consider urologic evaluation for underlying abnormalities, as these are common in patients with GBS UTI 3

Common Pitfalls to Avoid

• Dismissing low colony counts: Even 10,000-50,000 CFU/mL can represent true infection in symptomatic patients
• Failing to check susceptibility: Increasing resistance to non-beta-lactam antibiotics has been observed 7
• Missing underlying conditions: GBS UTI often signals underlying urinary tract abnormalities that require evaluation 3
• Inadequate treatment duration: Ensure complete resolution of infection to prevent recurrence or complications

Remember that GBS accounts for approximately 1-2% of positive urine cultures in non-pregnant adults 2, 3, and proper identification and treatment are essential to prevent invasive disease.