AKT · Renal & urology/Infection & obstruction

Urinary tract infection

Bacterial infection of the lower urinary tract — E. coli commonest (uropathogenic Enterobacteriaceae)

Overview

Infection of the bladder/urethra (lower UTI/cystitis), usually by E. coli. The high-yield distinctions are: who needs a culture vs empirical treatment, the antibiotic choice and DURATION (women 3 days, men 7 days — any male UTI is 'complicated'), pregnancy (treat asymptomatic bacteriuria, avoid trimethoprim 1st trimester / nitrofurantoin at term), and catheter-associated UTI.

Recognise

Dysuria, frequency, urgency, suprapubic pain, cloudy/offensive urine; haematuria; in the elderly may present as delirium/falls
Urine dipstick: nitrites (specific) + leucocytes; send culture if pregnant, male, recurrent, catheterised, treatment failure, or systemically unwell
Atypical/non-specific in the very young and very old; catheter-associated UTI is common

Red flags

Fever, loin pain, rigors or systemic upset → pyelonephritis/urosepsis → escalate (see pyelonephritis)
Pregnancy: treat asymptomatic bacteriuria (risk of pyelonephritis/preterm labour); recurrent/haematuria in older patients → exclude malignancy

Differentials & how to tell them apart

Pyelonephritisupper-tract — fever, loin pain, rigors, systemic upset (see its card)

Urethritis/STI (chlamydia, gonorrhoea)sexually active, discharge, sterile pyuria — cross-ref sexual_health

Vaginitis / interstitial cystitisdischarge/irritation; chronic pelvic pain with negative cultures

Asymptomatic bacteriuriapositive culture without symptoms — treat only in pregnancy (not the elderly/catheterised)

Investigations

Urine dipstick (nitrites/leucocytes) — but don't dipstick over-65s/catheterised (often positive without infection); MSU culture in pregnancy/men/recurrent/failure/catheter; bloods + cultures if systemically unwell; investigate recurrent UTI or persistent haematuria (imaging/cystoscopy to exclude stones/cancer).

Management

Nitrofurantoin/trimethoprim — women 3 days, men 7 days; pregnancy avoid trimethoprim 1st-tri / nitrofurantoin at term

1Diagnose from symptoms ± dipstick (send culture if pregnant/male/recurrent/catheterised/unwell). Treat non-pregnant women with nitrofurantoin or trimethoprim for 3 days; men for 7 days.Gate: Fever/loin pain/rigors/systemic upset → it's pyelonephritis/urosepsis, not simple cystitis — escalate. In pregnancy treat asymptomatic bacteriuria and avoid trimethoprim (1st trimester) and nitrofurantoin (at term).
2Catheter-associated symptomatic UTI → treat + change/remove the catheter (don't treat asymptomatic bacteriuria except in pregnancy). Investigate recurrent UTI or persistent haematuria for stones/malignancy.

Non-pregnant women: nitrofurantoin (if eGFR ≥45) or trimethoprim — 3 DAYS — first-line; trimethoprim only if low resistance risk

Men: nitrofurantoin or trimethoprim — 7 DAYS — any UTI in a man is 'complicated'; consider prostatitis

Pregnancy: nitrofurantoin (avoid at term) or cefalexin; AVOID trimethoprim in the 1st trimester (folate antagonist/NTD) — treat asymptomatic bacteriuria too; nitrofurantoin avoided near term (neonatal haemolysis)

Catheter-associated: change/remove the catheter + antibiotics if symptomatic — don't treat asymptomatic catheter bacteriuria

Key points

Lower UTI (E. coli) → nitrofurantoin/trimethoprim: women 3 DAYS, men 7 DAYS (male UTI = complicated, think prostatitis). Pregnancy: treat asymptomatic bacteriuria; AVOID trimethoprim 1st trimester (NTD) and nitrofurantoin at term (haemolysis). Don't dipstick/treat asymptomatic bacteriuria in the elderly/catheterised.

Monitor & prognosis

Symptom resolution, culture sensitivities, recurrence; pregnancy follow-up culture.

Excellent; complications are pyelonephritis, urosepsis and (in pregnancy) preterm labour.

Source: NICE NG109 (lower UTI); cross-ref sexual_health, O&G (pregnancy)