What is the recommended treatment for a patient with a urinary tract infection caused by Escherichia coli, as indicated by urinalysis and urine culture results showing greater than 100,000 CFU/mL of Escherichia coli?

Treatment of Urinary Tract Infection Caused by Escherichia coli

Based on the urinalysis and culture results showing E. coli with specific antibiotic susceptibilities, nitrofurantoin is the recommended first-line treatment for this urinary tract infection.

Interpretation of Laboratory Results

• The urinalysis shows clear signs of infection with 3+ leukocyte esterase, ≥60 WBCs/HPF, many bacteria, 1+ blood, and 1+ protein, confirming an active urinary tract infection 1
• The urine culture confirms >100,000 CFU/mL of Escherichia coli, which is the most common causative pathogen in urinary tract infections (75-95% of cases) 1
• The susceptibility testing shows the E. coli isolate is:
  • Susceptible to: nitrofurantoin, cefazolin, cefepime, ceftazidime, ceftriaxone, imipenem, meropenem, piperacillin/tazobactam, and trimethoprim/sulfamethoxazole
  • Resistant to: ciprofloxacin, levofloxacin, and gentamicin
  • Intermediate susceptibility to: amoxicillin/clavulanate and ampicillin/sulbactam 1

Treatment Recommendations

First-line Options (in order of preference):

1. Nitrofurantoin 100 mg twice daily for 5 days

   • Recommended as a first-choice option by multiple guidelines 1
   • The organism is susceptible to nitrofurantoin 2
   • Has maintained excellent activity against E. coli with low resistance rates (1.1-8.4%) 3, 4, 5
   • Achieves high urinary concentrations 2

2. Trimethoprim-sulfamethoxazole (TMP-SMX) 160/800 mg (double strength) twice daily for 3 days

   • Recommended as a first-choice option by guidelines 1
   • The organism is susceptible to TMP-SMX 6
   • Appropriate for urinary tract infections due to susceptible E. coli 6
   • Short course (3 days) is effective for uncomplicated cystitis 1

Alternative Options (if first-line agents cannot be used):

1. Cefazolin (parenteral) or an oral cephalosporin

   • The organism is susceptible to cefazolin and other cephalosporins 1
   • Oral cephalosporins are considered second-line options 2
   • Duration of 3-7 days depending on specific agent 1

2. Piperacillin-tazobactam (for complicated infections requiring IV therapy)

   • The organism is susceptible to this agent 1
   • Reserved for more severe infections or when oral therapy is not appropriate 1

Avoid These Agents (due to resistance):

• Fluoroquinolones (ciprofloxacin, levofloxacin): The organism is resistant to these agents 1
• Aminoglycosides (gentamicin): The organism is resistant to gentamicin 1
• Amoxicillin-clavulanate and ampicillin-sulbactam: The organism shows intermediate susceptibility, which may lead to treatment failure 2

Duration of Treatment

• For uncomplicated cystitis:

  • Nitrofurantoin: 5 days 1
  • TMP-SMX: 3 days 1
  • Oral cephalosporins: 3-5 days 1

• For complicated UTI or pyelonephritis:

  • Extend treatment to 7-14 days depending on severity and clinical response 1

Follow-up Recommendations

• Routine post-treatment urinalysis or urine cultures are not indicated for asymptomatic patients after treatment 1
• If symptoms do not resolve by the end of treatment or recur within 2 weeks, obtain a repeat urine culture and susceptibility testing 1
• For recurrent infections (≥3 episodes in 12 months), consider further evaluation for underlying abnormalities 1

Important Clinical Considerations

• Ensure adequate hydration to promote more frequent urination 1
• Encourage urge-initiated voiding and post-coital voiding if applicable 1
• For postmenopausal women, consider topical vaginal estrogens if appropriate 1
• Do not treat asymptomatic bacteriuria except in specific circumstances (pregnancy, prior to urologic procedures) 1

Common Pitfalls to Avoid

• Using fluoroquinolones empirically despite high resistance rates (>20% in many regions) 1, 5
• Treating for longer than necessary, which increases risk of adverse effects and antimicrobial resistance 1
• Failing to adjust therapy based on culture and susceptibility results 1
• Using broad-spectrum agents unnecessarily when narrower-spectrum options are effective 1, 2