Urinary Tract Infections

The patient says it burns when they urinate — but the difference between a lower UTI and urosepsis can be a matter of hours. Knowing where the infection sits changes everything you do next.

Urinary tract infections are classified by location: lower (cystitis, urethritis) versus upper (pyelonephritis). Lower UTIs present with dysuria, urgency, frequency, suprapubic discomfort, and cloudy or foul-smelling urine — but typically no fever. Pyelonephritis adds flank or costovertebral angle (CVA) tenderness, high fever (often >101°F/38.3°C), chills, nausea, and vomiting. This distinction drives the plan: lower UTIs are often treated with short-course oral antibiotics (trimethoprim-sulfamethoxazole for 3 days or nitrofurantoin for 5 days), while pyelonephritis may require IV antibiotics and hospitalization — nitrofurantoin is NOT appropriate for pyelonephritis because it does not achieve adequate renal tissue concentrations. A clean-catch midstream urine specimen is the gold standard for culture; catheterized specimens are used when clean-catch isn't feasible. Colony counts ≥100,000 CFU/mL confirm infection. E. coli causes approximately 80% of community-acquired UTIs. Risk factors include female anatomy (short urethra), indwelling catheters, urinary stasis, pregnancy, and immunosuppression. Catheter-associated UTIs (CAUTIs) are a leading hospital-acquired infection — removal of unnecessary catheters is the single most effective prevention strategy. Encourage fluid intake of 2–3 liters per day unless contraindicated, and teach women to wipe front to back and void after intercourse.

Key Distinctions

Don't confuse lower UTI (no fever, suprapubic pain) with pyelonephritis (fever, CVA tenderness) — the fever and flank pain are the dividing line. Students mistake cloudy urine alone as diagnostic; urine culture with ≥100,000 CFU/mL confirms infection. Asymptomatic bacteriuria in older adults does NOT automatically warrant antibiotics — treat only when symptoms are present, except in pregnancy.

Clinical Pearl

Fever plus flank pain equals pyelonephritis until proven otherwise. No fever and just burning? Think cystitis. The infection's zip code determines its severity.