Key Facts

UTI is one of the most common infections encountered in both primary and secondary care. Accurate diagnosis, appropriate antibiotic selection, and avoidance of overtreatment (especially of asymptomatic bacteriuria) are key principles.

Epidemiology

• ~50% of women experience at least one UTI in their lifetime
• Incidence: ~150 million UTIs globally/year
• Female:male ratio: ~8:1 in young adults; ratio narrows with age (BPH in men)
• Recurrent UTI: affects ~25% of women within 6 months of first episode
• CAUTI: accounts for ~40% of hospital-acquired infections

Aetiology

• E. coli: >80% of uncomplicated UTIs (uropathogenic strains — UPEC)
• Klebsiella pneumoniae: 5–10%
• Proteus mirabilis: associated with alkaline urine and staghorn calculi (urease producer)
• S. saprophyticus: young sexually active women (~5–15%)
• Enterococcus: associated with catheterisation, hospital acquisition
• Pseudomonas: catheter-associated, structural abnormalities

Pathophysiology

• Ascending infection: perineal bacteria → urethra → bladder (cystitis) → ureters → kidneys (pyelonephritis)
• UPEC express type 1 fimbriae (adhere to uroepithelium) and P fimbriae (ascend to kidneys)
• Shorter female urethra → increased susceptibility
• Risk factors: sexual intercourse, spermicides, post-menopausal atrophic changes, catheterisation, obstruction, vesicoureteric reflux, pregnancy, diabetes

Lower UTI (Cystitis)

• Dysuria (burning on urination)
• Frequency, urgency
• Suprapubic pain/discomfort
• Haematuria
• Cloudy, offensive-smelling urine
• Absence of systemic features

Upper UTI (Pyelonephritis)

• Loin/flank pain (often unilateral), renal angle tenderness
• High fever, rigors
• Nausea, vomiting
• Malaise
• May have preceding lower UTI symptoms

UTI in Elderly

• Often atypical: new confusion/delirium, falls, functional decline
• Do NOT treat asymptomatic bacteriuria in elderly — very common finding (up to 50% in care home residents)

Red Flags

• Signs of sepsis (tachycardia, hypotension, fever, confusion)
• Loin pain + fever (pyelonephritis)
• Haematuria in >60 years (possible malignancy — 2-week wait referral)
• UTI in pregnancy (pyelonephritis risk)
• Urinary retention
• Suspected obstruction (single kidney, known stones)

Bedside

• Urine dipstick: nitrites (most specific — ~95% specific), leucocytes (sensitive but non-specific)
  • Nitrite+ AND leucocyte+ → high probability of UTI
  • Nitrite– AND leucocyte– → UTI unlikely (NPV >95%)
• MSU for culture and sensitivity: send if complicated UTI, treatment failure, pregnancy, male, recurrent, catheterised
• Urine pregnancy test: if reproductive age

Bloods

• Not required for uncomplicated lower UTI
• FBC, CRP, U&Es, blood cultures: if pyelonephritis or sepsis
• Lactate: if sepsis suspected

Imaging

• Not routinely required for uncomplicated UTI
• Renal USS: if pyelonephritis not responding to treatment (exclude obstruction/abscess)
• CT KUB: if stones suspected
• USS/DMSA scan: recurrent UTIs in children (vesicoureteric reflux)

Special Tests

• Post-void residual volume: if recurrent UTIs (incomplete emptying)
• Cystoscopy: recurrent UTIs with haematuria (exclude malignancy)
• Urodynamics: if lower urinary tract symptoms with recurrent UTIs

Non-pharmacological

• Adequate hydration: encourage oral fluids
• Paracetamol/ibuprofen: for pain and fever
• Cranberry products: limited evidence; not recommended by NICE for prevention
• Vaginal oestrogen (post-menopausal): topical oestradiol cream reduces recurrent UTI
• Behavioural: void after intercourse, front-to-back wiping

Pharmacological

Uncomplicated lower UTI in women (NICE NG109):

• First-line: nitrofurantoin 100mg MR BD for 3 days
• Second-line: trimethoprim 200mg BD for 3 days (if low local resistance)
• Third-line: pivmecillinam 400mg stat then 200mg TDS for 3 days
• Avoid fluoroquinolones for uncomplicated UTI (reserve for serious infections)

Lower UTI in men:

• Trimethoprim 200mg BD for 7 days or nitrofurantoin 100mg MR BD for 7 days
• Consider prostatitis if recurrent — longer course required

Pyelonephritis:

• Mild (oral): cefalexin 500mg BD–TDS for 7–10 days, or co-amoxiclav 500/125mg TDS
• Severe (IV): co-amoxiclav 1.2g TDS IV, or gentamicin 5mg/kg OD IV + amoxicillin 1g TDS IV
• Switch to oral when improving; total 7–14 days

UTI in pregnancy:

• Treat all: including asymptomatic bacteriuria
• Nitrofurantoin (avoid at term — neonatal haemolysis), cefalexin, or amoxicillin (guided by sensitivities)
• Avoid trimethoprim in first trimester (folate antagonist)
• MSU culture at booking; treat positive results

Recurrent UTI (≥3/year):

• Antibiotic prophylaxis: nitrofurantoin 50–100mg ON or trimethoprim 100mg ON for 6 months, then review
• Post-coital prophylaxis: single-dose antibiotic after intercourse
• Vaginal oestrogen: topical oestradiol for post-menopausal women
• Self-start antibiotics: patient-initiated treatment with safety-netting

Referral Criteria

• Urology: recurrent UTIs in men (exclude structural cause), recurrent UTIs with haematuria
• Nephrology: recurrent pyelonephritis, renal scarring
• Gynaecology: post-menopausal vaginal atrophy management
• 2-week wait: visible haematuria in >60 years (exclude bladder cancer)

• Uncomplicated lower UTI: >90% cure with appropriate antibiotics
• Pyelonephritis: >95% recovery with treatment; ~5% develop bacteraemia
• Recurrent UTI: ~25% of women have recurrence within 6 months
• Prophylactic antibiotics: reduce recurrence by ~80%
• UTI in pregnancy: untreated bacteriuria → 20–30% develop pyelonephritis; treatment reduces this to <5%
• CAUTI: major source of morbidity; duration of catheterisation is the strongest risk factor
• Trimethoprim resistance in E. coli: ~30% in UK — use nitrofurantoin first-line

UTI Antibiotic Summary (NICE NG109)

Urine Dipstick Interpretation