Management of Coagulase-Negative Staphylococcus Bacteriuria in Asymptomatic Pregnant Women
No treatment is recommended for this patient. The colony count of 10,000-49,000 CFU/mL falls below the diagnostic threshold for asymptomatic bacteriuria in pregnancy, and coagulase-negative staphylococci (excluding S. saprophyticus) are typically urogenital contaminants rather than true pathogens.
Diagnostic Threshold Not Met
- Asymptomatic bacteriuria in pregnancy requires ≥10^5 (100,000) CFU/mL on urine culture for diagnosis 1, 2.
- This patient's culture shows only 10,000-49,000 CFU/mL, which is below the established threshold for treatment 1.
- The IDSA guidelines specifically state that two consecutive voided urine specimens with isolation of the same bacterial strain in quantitative counts ≥10^5 CFU/mL are required for diagnosis 2.
Organism Considerations
- Coagulase-negative staphylococci (other than S. saprophyticus) are common urogenital contaminants and rarely cause true urinary tract infections 3, 4.
- S. saprophyticus is the only coagulase-negative staphylococcus species that commonly causes UTIs, particularly in young women, and this organism has been specifically excluded in your case 3.
- In a study of pregnant women with asymptomatic bacteriuria, coagulase-negative staphylococci represented only 6.4% of true pathogens, and these were predominantly contaminants 5.
Why Treatment Would Be Inappropriate
- Treating low colony counts and likely contaminants exposes the patient to unnecessary antibiotic risks without proven benefit 1.
- The robust evidence supporting treatment of asymptomatic bacteriuria in pregnancy applies only to colony counts ≥10^5 CFU/mL, where untreated bacteriuria carries a 20-30 fold increased risk of pyelonephritis 1, 2.
- Treatment of true asymptomatic bacteriuria reduces pyelonephritis risk from 20-35% to 1-4%, but this benefit has only been demonstrated at the ≥10^5 CFU/mL threshold 1.
Recommended Management Approach
Repeat urine culture if clinical concern persists:
- If there is genuine concern about urinary tract infection despite the patient being asymptomatic, obtain a repeat clean-catch midstream urine culture 2.
- Ensure proper collection technique to minimize contamination, as coagulase-negative staphylococci are common skin flora 4.
Continue routine prenatal screening:
- All pregnant women should be screened for asymptomatic bacteriuria with urine culture at least once during early pregnancy (12-16 weeks gestation or at first prenatal visit) 2.
- If this was the routine screening culture, no further action is needed at this time 2.
Common Pitfalls to Avoid
- Do not treat based on colony counts below 10^5 CFU/mL unless the patient is symptomatic, as this represents overtreatment 1.
- Do not assume all bacteria in urine represent infection—coagulase-negative staphylococci are frequently contaminants, especially at low colony counts 3, 4.
- Pyuria alone without bacteriuria is not an indication for treatment in asymptomatic patients 2.
- Avoid empiric treatment without meeting diagnostic criteria, as this contributes to antimicrobial resistance without improving maternal or fetal outcomes 5.