Do we treat asymptomatic bacteriuria in pregnancy?

Treatment of Asymptomatic Bacteriuria in Pregnancy

Yes, asymptomatic bacteriuria in pregnancy should be screened for and treated with antibiotics. This recommendation is strongly supported by guidelines from the Infectious Diseases Society of America (IDSA), U.S. Preventive Services Task Force (USPSTF), and American College of Obstetricians and Gynecologists (ACOG) 1.

Rationale for Treatment

• Untreated asymptomatic bacteriuria increases the risk of pyelonephritis 20-30 fold in pregnant women 1
• Treatment reduces the incidence of pyelonephritis from 20-35% to 1-4% 1
• Treatment is associated with a reduction in low birthweight babies (RR 0.66,95% CI 0.49-0.89) 2
• Implementation of screening and treatment programs has demonstrated significant reductions in pyelonephritis rates (from 1.8% to 0.6% and from 2.1% to 0.5%) 1

Screening Recommendations

• All pregnant women should be screened for asymptomatic bacteriuria at least once in early pregnancy
• Optimal timing is at 12-16 weeks gestation 1
• Urine culture is the gold standard for diagnosis 1, 3
• Dipstick testing for pyuria has low sensitivity (approximately 50%) and should not be used as the sole screening method 1, 3

Diagnostic Criteria

Asymptomatic bacteriuria is defined as:

• 2 consecutive voided urine specimens with isolation of the same bacterial strain in quantitative counts ≥10^5 CFU/mL, OR
• A single catheterized urine specimen with 1 bacterial species isolated in a quantitative count ≥10^2 CFU/mL 1

Treatment Protocol

1. Antibiotic Selection:

   • First-line options: nitrofurantoin 100mg BID, cephalexin 500mg QID, or ampicillin 500mg QID (if susceptible) 1
   • Avoid fluoroquinolones, tetracyclines, and trimethoprim-sulfamethoxazole in the first and third trimesters 1
   • Base selection on culture and sensitivity results whenever possible 3

2. Treatment Duration:

   • Use a 3-7 day course of antibiotics 1
   • Seven-day regimens provide better microbiological cure rates than single-dose treatments 4
   • High-quality evidence shows better cure rates with short (4-7 day) regimens compared to single-dose therapy (RR 1.72,95% CI 1.27-2.33) 4

3. Follow-up:

   • Obtain follow-up urine culture 1-2 weeks after completing therapy 1
   • If bacteriuria persists, retreat with a different antibiotic based on susceptibility 1
   • Periodic screening for recurrent bacteriuria should be undertaken following therapy 1

Common Pitfalls to Avoid

• Inadequate screening (using dipstick instead of culture)
• Insufficient treatment duration (single-dose therapy)
• Inappropriate antibiotic selection
• Failure to follow up with post-treatment culture
• Overtreatment without proper diagnosis 1

The most common causative organism is Escherichia coli, accounting for approximately 79% of cases 5, 6. This underscores the importance of antibiotic selection that covers gram-negative organisms.

While there is some debate about the impact of treated pyelonephritis on adverse fetal outcomes 6, the evidence clearly supports screening and treating asymptomatic bacteriuria to prevent pyelonephritis and reduce the risk of low birthweight infants 1, 2.