Bacterial infection of the bladder (cystitis) or upper tract (pyelonephritis). Most common pathogen: E. coli.
⚠ Red flags
- Sepsis: HR >100, BP <90, confusion, lactate >2
- Obstruction (stone, catheter block) — urgent decompression
- Pregnancy — treat all bacteriuria including asymptomatic
- Immunosuppression, transplant, or pregnancy with pyelonephritis — admit
Diagnostic criteria
Clinical
- Lower UTI: dysuria, frequency, urgency, suprapubic pain
- Upper UTI: fever, rigors, loin pain, nausea/vomiting
Investigations
- Urine dipstick: nitrites and leucocytes (high sensitivity in symptomatic patients)
- MSU culture and sensitivity (gold standard; send before antibiotics if complicated)
Investigations
Essential
- MSU culture and sensitivity
Optional
- FBC, CRP, U&E, creatinine if systemically unwell
- Blood cultures if pyelonephritis or sepsis
- Renal USS if recurrent UTI, suspected obstruction, or poor response
- CT-KUB if stone or pyonephrosis suspected
Management
Acute
- Pyelonephritis with sepsis: IV antibiotics, fluid resuscitation, source control
Long-term
- Recurrent UTI: low-dose nightly prophylaxis (trimethoprim 100 mg or nitrofurantoin 50 mg) for 6 months
- Vaginal oestrogen for post-menopausal recurrent UTI
Non-pharmacological
- Encourage fluid intake (≥2 L/day)
- Post-coital voiding; avoid spermicidal contraception in recurrent UTI
Pharmacological
| Drug | Dose | Notes |
|---|---|---|
| Nitrofurantoin | 100 mg PO BD for 3 days (women) or 7 days (men) | First-line uncomplicated cystitis. Avoid if eGFR <45. |
| Trimethoprim | 200 mg PO BD for 3–7 days | Alternative; avoid in 1st trimester pregnancy and check local resistance. |
| Ciprofloxacin | 500 mg PO BD for 7 days | For complicated UTI / outpatient pyelonephritis. Tendon and QT risks; avoid in pregnancy. |
| Ceftriaxone (IV) | 1–2 g IV once daily | Inpatient pyelonephritis; switch to oral when sensitivities known and patient stable. |
Monitoring
- Symptom resolution within 48–72h of antibiotics
- Test of cure culture only in pregnancy, recurrent UTI, or pyelonephritis
Referral criteria
- Recurrent UTI ≥3 episodes/year
- Suspected upper tract obstruction or stones
- Persistent haematuria after treatment (urology — exclude malignancy)
- Pregnancy with pyelonephritis
Complications
- Pyelonephritis, perinephric abscess
- Urosepsis
- Renal scarring (especially in children with VUR)
- Preterm labour (untreated UTI in pregnancy)
Special populations
- Pregnancy
- Treat asymptomatic bacteriuria. Avoid trimethoprim in 1st trimester (folate antagonist), nitrofurantoin near term (haemolysis). Cefalexin generally safe.
- Renal impairment
- Avoid nitrofurantoin if eGFR <45. Adjust ciprofloxacin and beta-lactam doses.
- Hepatic impairment
- Most antibiotics safe; review co-amoxiclav use in active liver disease.
- Elderly
- Asymptomatic bacteriuria common — do NOT treat unless symptomatic. Beware atypical presentation (delirium).
- Paediatric
- Send clean-catch MSU; consider USS in <6 months or recurrent UTI to look for VUR.