Urinary Tract Infection

Bacterial infection of the urinary tract: lower UTI/cystitis (bladder) or upper UTI/pyelonephritis (kidney, more severe).

Predominantly E. coli (~80%), also Klebsiella, Proteus, Enterococcus, Staph saprophyticus (young sexually active women).

Classified: uncomplicated (healthy non-pregnant women, normal urinary tract) vs. complicated (male, pregnant, catheter, structural/functional abnormality, immunocompromised, recent instrumentation).

• Cystitis: dysuria, frequency, urgency, suprapubic pain, hematuria: no fever/flank pain/systemic symptoms

• Pyelonephritis: fever, rigors, flank/loin pain, costovertebral angle tenderness, nausea/vomiting, plus lower UTI symptoms often present; can progress to sepsis (see Sepsis entry)

• Elderly: may present atypically: confusion, falls, functional decline, without classic urinary symptoms

• Catheter-associated: often asymptomatic bacteriuria (do NOT treat unless symptomatic) vs. true infection (fever, new flank pain, altered mental status without other cause)

• Uncomplicated cystitis in women with classic symptoms: clinical diagnosis sufficient, treat empirically without culture
• Urine dipstick: nitrites (specific) and leukocyte esterase (sensitive), supportive, not required if classic symptoms present
• Urine culture: indicated for pyelonephritis, complicated UTI, treatment failure, recurrent UTI, pregnancy, men, catheterized patients, guides targeted therapy
• Bloods (FBC, U&E, CRP, blood cultures): if systemically unwell/pyelonephritis/suspected sepsis
• Imaging (renal ultrasound/CT): recurrent pyelonephritis, suspected obstruction/stone, failure to respond to treatment, males with first UTI (investigate underlying cause)
• Asymptomatic bacteriuria: do not treat except in pregnancy or pre-urological instrumentation

Differentials: vaginitis/candidiasis (external dysuria, discharge), urethritis (STI-related), interstitial cystitis, pelvic inflammatory disease, appendicitis/renal colic (flank pain differentials), STI.

Uncomplicated cystitis (women):

• Nitrofurantoin 100mg bd × 3-5 days (avoid if eGFR <45), or trimethoprim 200mg bd × 3 days (check local resistance), or fosfomycin 3g single dose
• Increase fluid intake, urinary alkalinizers for symptom relief (limited evidence)

Pyelonephritis:

• Outpatient (mild, tolerating oral, no red flags): oral ciprofloxacin 500mg bd × 7 days, or co-amoxiclav/cephalosporin per local resistance × 7-14 days
• Inpatient (severe, vomiting, sepsis features, pregnancy): IV antibiotics (ceftriaxone, or ciprofloxacin), switch to oral once improving, total course 10-14 days
• Identify/manage complications: renal/perinephric abscess (imaging if not improving in 48-72h), obstruction requiring drainage (stent/nephrostomy)

Recurrent UTI (≥2 in 6 months or ≥3 in 12 months): investigate underlying cause, post-coital prophylaxis if coitally-related, low-dose nightly prophylactic antibiotic (nitrofurantoin 50-100mg nocte) if conservative measures fail, vaginal estrogen in postmenopausal women (restores protective flora), consider methenamine hippurate as non-antibiotic option.

Men: always investigate for underlying cause (prostatic, structural) after first UTI, not considered "uncomplicated"; treat 7 days minimum, consider prostatitis if perineal pain/systemic symptoms (requires longer course, 2-4 weeks, quinolone/trimethoprim given prostate penetration).

Pregnancy: treat all bacteriuria (symptomatic and asymptomatic) (nitrofurantoin (avoid near term) neonatal hemolysis risk) or cephalexin; avoid trimethoprim in first trimester (folate antagonist) and avoid quinolones throughout.

Referral: urology for recurrent UTI in men, structural abnormality, stones, treatment-resistant disease; nephrology for recurrent pyelonephritis with renal impairment.