A 28-year-old woman from Delhi presents to the emergency department with acute onset dysuria, frequency, and suprapubic pain for 2 days. She denies fever, flank pain, or vaginal discharge. Urinalysis shows pyuria (>10 WBC/hpf), bacteriuria, and nitrites. Urine culture is pending. Blood pressure is 120/80 mmHg, temperature 37.2°C. On direct Gram stain of uncentrifuged urine, Gram-negative rods are seen. Which of the following is the most likely organism and the most appropriate empirical antibiotic for uncomplicated acute cystitis in this patient?

Explanation

## Clinical Diagnosis **Key Point:** Uncomplicated acute cystitis in a non-pregnant, non-immunocompromised woman is most commonly caused by uropathogenic E. coli (UPEC), accounting for 80–90% of community-acquired UTI cases. ## Organism Identification | Feature | E. coli | Klebsiella | Proteus | Pseudomonas | | --- | --- | --- | --- | --- | | **Frequency in uncomplicated UTI** | 80–90% | 5–10% | 2–5% | <1% (nosocomial) | | **Nitrite test** | Positive | Positive | Positive | Negative | | **Motility** | Non-motile (most strains) | Non-motile | Highly motile (swarming) | Motile | | **Indole production** | Positive | Negative | Negative | Negative | | **Typical setting** | Community-acquired | Hospital/complicated | Complicated/stones | Nosocomial/immunocompromised | ## Treatment of Uncomplicated Cystitis **High-Yield:** First-line agents for uncomplicated acute cystitis are: 1. **Nitrofurantoin** 100 mg twice daily × 5 days (preferred in most guidelines) 2. **Trimethoprim-sulfamethoxazole** (TMP-SMX) 160/800 mg twice daily × 3 days (if local resistance <20%) 3. **Fosfomycin** 3 g single dose (excellent for resistant organisms) 4. **Fluoroquinolone** (reserved for complicated UTI or allergy to above) **Clinical Pearl:** Nitrofurantoin is preferred for uncomplicated cystitis because: - Achieves high urinary concentrations - Minimal systemic absorption - Excellent E. coli coverage - Low collateral damage to normal flora - Cost-effective - Short 5-day course reduces resistance **Warning:** Nitrofurantoin is contraindicated in renal impairment (eGFR <30 mL/min) and should be avoided in pregnancy (risk of hemolytic anemia in G6PD deficiency). ## Why Other Options Are Incorrect Cephalosporins (ceftriaxone) and beta-lactam/beta-lactamase inhibitors (piperacillin-tazobactam) are reserved for complicated UTI, pyelonephritis, or nosocomial infection. Fluoroquinolones should be reserved due to resistance concerns and adverse effects. Proteus and Pseudomonas are uncommon in uncomplicated community-acquired cystitis and suggest underlying anatomic abnormality or nosocomial acquisition.