Urinary Tract Infection
Summary
Urinary tract infection (UTI) is infection of the urinary system, most commonly the bladder (cystitis). It is one of the most frequent bacterial infections, particularly in women. Most are caused by Escherichia coli ascending from the perineum. Classic symptoms include dysuria, frequency, urgency, and suprapubic pain. Diagnosis is clinical in uncomplicated cases; urine culture is indicated for complicated UTI, pregnancy, or recurrence. First-line treatment is a short course of antibiotics (nitrofurantoin or trimethoprim for 3-7 days). Upper UTI (pyelonephritis) requires longer treatment. Recurrent UTI warrants investigation in some patients.
Key Facts
- Definition: Bacterial infection of the urinary tract (lower = cystitis; upper = pyelonephritis)
- Incidence: 50% of women will have at least one UTI in their lifetime
- Demographics: F:M 30:1 in young adults; equalises in elderly
- Pathognomonic: Dysuria + frequency + significant bacteriuria
- Gold Standard Investigation: Urine culture (but clinical diagnosis often sufficient for simple UTI)
- First-line Treatment: Nitrofurantoin 100mg BD x 3 days OR Trimethoprim 200mg BD x 3 days
- Prognosis: Excellent with treatment; recurrence common
Clinical Pearls
Short Course Pearl: Uncomplicated cystitis in women requires only 3 days of treatment. Longer courses increase side effects without improving outcomes.
Nitrofurantoin Pearl: Nitrofurantoin is first-line (low resistance). Avoid if eGFR less than 45 (reduced efficacy) or at term pregnancy.
Male UTI Pearl: All UTIs in men are considered complicated by definition. Require 7 days treatment minimum and investigation for underlying cause.
Asymptomatic Bacteriuria Pearl: Do NOT treat asymptomatic bacteriuria except in pregnancy (risk of pyelonephritis and preterm labour).
Catheter Pearl: Catheter-associated UTI requires clinical symptoms for diagnosis - bacteriuria alone is not UTI.
Why This Matters Clinically
UTI is one of the most common reasons for antibiotic prescriptions. Appropriate diagnosis, sensible antibiotic choice and duration, avoiding treatment of asymptomatic bacteriuria, and identifying patients who need further investigation are key to good stewardship.
Incidence
| Population | Lifetime Risk |
|---|---|
| Women | 50% |
| Men | 5-10% |
| Elderly (both) | Increased |
Risk Factors
| Category | Factors |
|---|---|
| Female | Sexual activity, spermicide use, post-menopause (oestrogen deficiency), pregnancy |
| Anatomical | Short urethra (women), urological abnormalities, stones, obstruction |
| Catheterisation | Major risk factor for complicated UTI |
| Immunocompromised | Diabetes, immunosuppression |
| Male | Prostatic hypertrophy, urological surgery |
Classification
| Type | Definition |
|---|---|
| Uncomplicated | Cystitis in otherwise healthy, non-pregnant woman |
| Complicated | UTI with risk of treatment failure: male, pregnant, anatomical abnormality, catheter, stones, renal transplant, diabetes |
| Pyelonephritis | Upper urinary tract infection (kidney) |
| Recurrent | 2+ infections in 6 months OR 3+ in 12 months |
Mechanism
Step 1: Colonisation
- Ascension of uropathogens from perineum to urethra
- E. coli most common (75-95%)
- Virulence factors: type 1 and P fimbriae for adhesion
Step 2: Bladder Colonisation
- Bacteria reach bladder (short urethra in women = higher risk)
- Adherence to uroepithelium
- Overwhelm host defences (urination, mucosal immunity)
Step 3: Infection and Inflammation
- Bacterial replication
- Inflammatory response
- Symptoms: dysuria, frequency, urgency
Step 4: Complications
- Ascending infection → pyelonephritis
- Bacteraemia → urosepsis
- Chronic/recurrent infection
Causative Organisms
| Organism | Frequency | Notes |
|---|---|---|
| Escherichia coli | 75-95% | Most common |
| Klebsiella pneumoniae | 5-10% | Gram-negative |
| Proteus mirabilis | 5% | Associated with stones (urease producer) |
| Staphylococcus saprophyticus | 5-10% (young women) | Second most common in young women |
| Enterococcus faecalis | 5% | More common in CAUTI |
| Pseudomonas aeruginosa | CAUTI, complicated | Hospital-acquired |
Lower UTI (Cystitis)
| Symptom | Frequency |
|---|---|
| Dysuria | 90% |
| Frequency | 85% |
| Urgency | 80% |
| Suprapubic pain | 60% |
| Haematuria | 20-30% |
| Cloudy/malodorous urine | Variable |
Upper UTI (Pyelonephritis)
| Symptom | Frequency |
|---|---|
| Loin/flank pain | 80% |
| Fever/rigors | 80% |
| Nausea/vomiting | 60% |
| Lower UTI symptoms | Often present |
Red Flags
[!CAUTION]
- Fever, rigors, loin pain (pyelonephritis)
- Signs of sepsis
- Urinary retention
- Male patient
- Pregnancy
- Recurrent UTI
- Failed initial treatment
Atypical Presentations
Lower UTI
- Often normal
- May have suprapubic tenderness
- No fever (if fever, consider upper UTI)
Upper UTI (Pyelonephritis)
- Fever
- Renal angle tenderness (loin pain on palpation)
- Signs of sepsis if severe
Male UTI
- Examine for prostatitis (tender prostate on DRE)
- Assess for urinary retention
- Testicular/epididymal examination
Dipstick Testing
| Finding | Interpretation |
|---|---|
| Leucocyte esterase | Suggests WBCs (pyuria) |
| Nitrites | Suggests bacteria (E. coli, Klebsiella, Proteus) |
| Both positive | High positive predictive value |
| Both negative | Unlikely UTI (high negative predictive value) |
Urine Culture
When to send:
- Complicated UTI
- Pregnancy
- Male UTI
- Recurrent UTI
- Treatment failure
- Before starting antibiotics if possible
Significant bacteriuria:
- Greater than 10^5 CFU/mL (mid-stream urine)
- Lower counts may be significant in symptomatic patients
Blood Tests (if unwell)
- FBC: raised WCC
- CRP: elevated
- U&E: renal function (especially in pyelonephritis/sepsis)
- Blood cultures: if pyelonephritis or sepsis suspected
Imaging
| Indication | Modality |
|---|---|
| Complicated pyelonephritis | CT KUB (rule out abscess, obstruction) |
| Male UTI | Ultrasound (post-void residual, prostatic assessment) |
| Recurrent UTI | Ultrasound KUB ± cystoscopy |
Management Algorithm
SUSPECTED UTI
↓
┌─────────────────────────────────────────────────────────┐
│ ASSESS PATIENT TYPE │
├─────────────────────────────────────────────────────────┤
│ Uncomplicated (non-pregnant woman) → Treat empirically │
│ Complicated (male, pregnant, catheter) → Culture first │
│ Pyelonephritis/sepsis → Culture + longer treatment │
└─────────────────────────────────────────────────────────┘
↓
┌─────────────────────────────────────────────────────────┐
│ UNCOMPLICATED CYSTITIS (WOMEN) │
│ FIRST-LINE (3 days): │
│ - Nitrofurantoin 100mg BD (avoid if eGFR less than 45) │
│ - Trimethoprim 200mg BD (avoid if resistance greater │
│ than 20%) │
│ SECOND-LINE: │
│ - Fosfomycin 3g single dose │
│ - Pivmecillinam 400mg TDS x 3 days │
└─────────────────────────────────────────────────────────┘
↓
┌─────────────────────────────────────────────────────────┐
│ MALE UTI (7 days) │
│ Trimethoprim 200mg BD OR │
│ Nitrofurantoin 100mg BD │
│ + Investigate (ultrasound, PSA) │
└─────────────────────────────────────────────────────────┘
↓
┌─────────────────────────────────────────────────────────┐
│ PYELONEPHRITIS (7-10 days) │
│ Oral (if mild): Ciprofloxacin 500mg BD OR │
│ Co-amoxiclav 625mg TDS │
│ IV (if severe): Gentamicin OR IV co-amoxiclav │
│ Duration: 7-14 days │
└─────────────────────────────────────────────────────────┘
↓
┌─────────────────────────────────────────────────────────┐
│ PREGNANCY │
│ Always culture │
│ Safe antibiotics: Nitrofurantoin (avoid at term), │
│ Amoxicillin, Cefalexin │
│ Avoid: Trimethoprim (1st trimester), Quinolones │
│ Duration: 7 days │
└─────────────────────────────────────────────────────────┘
Antibiotic Choices
| Condition | First-Line | Duration |
|---|---|---|
| Uncomplicated cystitis (women) | Nitrofurantoin 100mg BD | 3 days |
| Male UTI | Trimethoprim 200mg BD | 7 days |
| Pregnancy | Nitrofurantoin (avoid at term) | 7 days |
| Pyelonephritis (mild) | Ciprofloxacin 500mg BD | 7-10 days |
| Pyelonephritis (severe) | IV gentamicin + amoxicillin | 10-14 days |
Recurrent UTI Prevention
| Strategy | Notes |
|---|---|
| Behavioural | Post-coital voiding, adequate hydration |
| Cranberry products | Modest evidence |
| Vaginal oestrogen | For postmenopausal women |
| Prophylactic antibiotics | Low-dose nightly or post-coital (specialist) |
| D-mannose | Some evidence; alternative |
Catheter-Associated UTI
- Only treat if symptomatic (not bacteriuria alone)
- Consider catheter change
- Treat for 7 days
| Complication | Features | Management |
|---|---|---|
| Pyelonephritis | Loin pain, fever, sepsis | Antibiotics, admission if severe |
| Urosepsis | Systemic infection | Sepsis 6, IV antibiotics |
| Perinephric abscess | Persistent fever, CT finding | Drainage |
| Chronic pyelonephritis | Recurrent infections, scarring | Prevention, investigation |
- Uncomplicated UTI: resolves quickly with treatment
- Pyelonephritis: good prognosis with treatment; risk of sepsis if delayed
- Recurrence rate: 20-30% within 6 months
Key Guidelines
-
NICE Guideline NG109. Urinary tract infection (lower): antimicrobial prescribing — 2018
-
NICE Guideline NG111. Pyelonephritis: antimicrobial prescribing — 2018
-
PHE. Management of infection guidance for primary care — UKHSA (for local resistance data)
-
EAU Guidelines on Urological Infections — 2023
Key Evidence
- Short-course (3-day) therapy as effective as longer courses for uncomplicated cystitis in women
- Nitrofurantoin and fosfomycin maintain low resistance rates
What is a UTI?
A UTI is an infection in your bladder or urinary system, usually caused by bacteria. It's very common, especially in women.
What are the symptoms?
- Pain or burning when you pass urine
- Needing to go frequently or urgently
- Lower abdominal pain
- Cloudy or smelly urine
Treatment
A short course of antibiotics (usually 3 days) will clear the infection. Take all the tablets even if you feel better.
When to seek help
- Fever, back pain, or feeling very unwell (could be kidney infection)
- Not improving after 48 hours
- Blood in urine
Prevention
- Drink plenty of fluids
- Wipe front to back
- Urinate after sex
- Don't delay going to the toilet
-
NICE Guideline NG109. Urinary tract infection (lower): antimicrobial prescribing. 2018.
-
NICE Guideline NG111. Pyelonephritis (acute): antimicrobial prescribing. 2018.
-
Bonkat G et al. EAU Guidelines on Urological Infections. Eur Assoc Urol. 2023.
-
Foxman B. Epidemiology of urinary tract infections. Nat Rev Urol. 2010;7(12):653-660. PMID: 21139641
-
Gupta K et al. International Clinical Practice Guidelines for Uncomplicated Cystitis and Pyelonephritis (IDSA). Clin Infect Dis. 2011;52(5):e103-e120. PMID: 21292654
-
PHE. Management of infection guidance for primary care. 2023.
Viva Points
"UTI presents with dysuria, frequency, urgency. Diagnose clinically in uncomplicated cystitis; culture for complicated. First-line: nitrofurantoin 100mg BD x 3 days. Male UTI = complicated, needs 7 days + investigation. Pyelonephritis: loin pain, fever - treat 7-14 days. Don't treat asymptomatic bacteriuria except pregnancy."
Common Mistakes
- ❌ Treating asymptomatic bacteriuria
- ❌ Using wrong duration (3 days is enough for simple cystitis)
- ❌ Not investigating male UTI
- ❌ Using nitrofurantoin in poor renal function
- ❌ Diagnosing UTI in elderly based on confusion alone
Last Reviewed: 2026-01-01 | MedVellum Editorial Team