What is the appropriate treatment for a patient with an uncomplicated urinary tract infection (UTI) caused by Escherichia coli (E. coli)?

Treatment of E. coli Urinary Tract Infection Based on Susceptibility Testing

For this patient with a urinary tract infection caused by multidrug-resistant E. coli, nitrofurantoin or meropenem are the most appropriate treatment options based on the susceptibility testing results.

Interpreting the Urinalysis and Culture Results

The urinalysis shows clear evidence of a urinary tract infection:

• Positive nitrites
• 3+ leukocyte esterase
• ≥60 WBCs/HPF
• Many bacteria

The urine culture confirms:

• E. coli with >100,000 CFU/mL
• Multidrug-resistant pattern with susceptibility only to:
  • Imipenem (S)
  • Meropenem (S)
  • Nitrofurantoin (S)
  • Piperacillin/tazobactam (S)

Treatment Algorithm Based on Susceptibility

First-line options (based on susceptibility):

1. Nitrofurantoin - Preferred for uncomplicated UTI

   • Dosing: 100 mg PO BID for 5-7 days
   • Advantages: Minimal resistance development, concentrated in urine 1
   • Limitations: Not for pyelonephritis or systemic infection

2. Meropenem - For complicated UTI or pyelonephritis

   • Dosing: 1 g IV q8h
   • Advantages: Highly effective against MDR organisms 2
   • Limitations: Requires IV administration, should be reserved for severe infections

Alternative options:

1. Piperacillin/tazobactam - For complicated UTI

   • Dosing: 3.375 g IV q6h or 4.5 g IV q8h
   • Advantages: Good coverage for complicated UTIs 2
   • Limitations: IV administration required

2. Imipenem - For complicated UTI

   • Dosing: 500 mg IV q6h
   • Advantages: Effective against MDR organisms 2
   • Limitations: IV administration, higher risk of seizures than meropenem

Decision-Making Factors

Uncomplicated vs. Complicated UTI

• If uncomplicated (no fever, flank pain, or systemic symptoms):

  • Nitrofurantoin is the preferred choice 1
  • Duration: 5 days

• If complicated (presence of fever, flank pain, systemic symptoms, or male patient):

  • Meropenem is the preferred choice 2
  • Duration: 7-14 days depending on severity

Special Considerations

• Carbapenem stewardship: The European Society of Clinical Microbiology and Infectious Diseases (ESCMID) recommends reserving carbapenems for severe infections 2
• For uncomplicated UTIs, even with resistant organisms, nitrofurantoin remains effective due to high urinary concentrations 1, 3

Antibiotic Resistance Context

This E. coli isolate shows an ESBL (Extended-Spectrum Beta-Lactamase) pattern with resistance to:

• All cephalosporins (cefazolin, cefepime, ceftazidime, ceftriaxone)
• Fluoroquinolones (ciprofloxacin, levofloxacin)
• Aminoglycosides (gentamicin)
• Trimethoprim/sulfamethoxazole

This resistance pattern is increasingly common, with studies showing rising ESBL prevalence from 0.1% in 2004 to 2.2% in 2014 4. The European Association of Urology guidelines note that local resistance patterns should guide empiric therapy, with nitrofurantoin remaining effective against most resistant E. coli strains 2, 5.

Follow-up Recommendations

• No routine post-treatment urinalysis or urine cultures are indicated for asymptomatic patients 2
• If symptoms persist after treatment completion, obtain a repeat urine culture
• For patients with recurrent UTIs, consider using prior culture results to guide future empiric therapy, as they have good predictive value for susceptibility patterns 6

Important Caveats

• Avoid fluoroquinolones for empiric therapy due to increasing resistance rates and adverse effects 1, 7
• Consider renal function when dosing antibiotics, particularly carbapenems and nitrofurantoin
• Nitrofurantoin should not be used if pyelonephritis is suspected, as it does not achieve adequate tissue concentrations 1
• Reserve carbapenems for severe infections to prevent further resistance development 2