A lower urinary tract infection (UTI) is an infection of the bladder usually by bacteria, but rarely by other microorganisms such as fungi, viruses, or parasites. Upper UTI includes pyelitis (infection of the proximal part of the ureters) and pyelonephritis (infection of the kidneys and the proximal part of the ureters).
Definitions
- Uncomplicated UTI: Infection in a person with normal urinary tract and kidney function
- Complicated UTI: When risk factors are present that predispose to persistent/recurrent infection or treatment failure
- Recurrent UTI: 3+ UTIs in last 12 months or 2+ episodes in last 6 months
- Asymptomatic bacteriuria: Significant bacteria in urine without symptoms
Risk Factors for Complicated UTI
- Structural/neurological urinary tract abnormalities
- Urinary catheters
- Virulent/atypical organisms
- Pregnancy
- Poorly controlled diabetes or immunosuppression
Causes
UTI results from pathogenic organisms gaining access to the urinary tract:
- Retrograde, ascending through urethra
- Via bloodstream (immunocompromised)
- Direct (catheterization, instrumentation, surgery)
Common Causative Microorganisms
Escherichia coli
80% of cases
Staphylococcus saprophyticus
4% of cases
Klebsiella pneumoniae
4% of cases
Proteus mirabilis
4% of cases
Less Common Pathogens
- Enterobacter, Enterococcus, Serratia, Pseudomonas, Staphylococcus aureus
- Candida albicans (in catheterized/immunocompromised)
Risk Factors in Men
- Age >50 years
- BPH or other obstruction (30% of young men with UTI have abnormalities)
- Catheterization (most common hospital-acquired infection)
- Previous instrumentation/surgery
- Previous UTI (risk increases with each infection)
Clinical Features
Classic Symptoms
- Dysuria (pain/burning during urination)
- Frequency
- Urgency
- Nocturia
- Suprapubic tenderness
- Cloudy/foul-smelling urine
- Haematuria
Atypical Presentations
- Elderly/frail patients
- Cognitive impairment
- Catheterized patients
- Delirium, lethargy, fever
- Incontinence
- Reduced ADL performance
- Anorexia
Suspect pyelonephritis if: Fever, loin pain, or rigors present
Differential Diagnosis
Women
- Pyelonephritis
- Vaginitis/lichen conditions
- STIs (chlamydia, gonorrhea)
- Urolithiasis
- Interstitial cystitis
- Malignancy
- Ectopic pregnancy
Men
- Acute prostatitis
- Bladder/renal cancer
- Epididymitis
- Pyelonephritis
- STIs
- Urethritis
- BPH
Investigations
In Women
| Dipstick Result |
Interpretation |
Action |
| Positive for nitrite OR leukocyte + RBC |
UTI likely |
Send culture if treatment failed/resistance possible |
| Negative nitrite + positive leukocyte |
UTI equally likely |
Send culture to confirm |
| Negative for all |
UTI unlikely |
Consider other diagnoses |
Always Send Urine Culture If:
- Pregnant
- Age >65 years
- Persistent symptoms
- Recurrent UTI
- Catheterized/recent catheter
- Risk factors for resistance
- Atypical symptoms
- Haematuria
In Men
- Confirm diagnosis with urine culture before treatment
- Dipsticks unreliable - only helpful if negative in mild symptoms
- Do not use dipsticks in catheterized or >65 years
Management
Admit If:
- Systemic symptoms (fever, rigors, vomiting, confusion)
- Dehydrated/unable to tolerate oral intake
General Measures
- Simple analgesia (paracetamol/ibuprofen)
- Adequate fluid intake
Antibiotic Treatment
Women
- First-line: Nitrofurantoin 100mg MR bd for 3d (if eGFR ≥45) OR Trimethoprim 200mg bd for 3d
- Consider delayed prescription for mild symptoms
Men
- First-line: Trimethoprim 200mg bd for 7d OR Nitrofurantoin 100mg MR bd for 7d
- Base on local resistance patterns
Advise all patients to seek urgent review if symptoms worsen or fail to improve within 48 hours
Special Scenarios
| Scenario |
Management |
| Catheter-associated UTI |
- Remove/change catheter if in >7 days
- Nitrofurantoin 100mg MR bd for 7d OR Trimethoprim 200mg bd for 7d OR Amoxicillin 500mg tds for 7d
|
| UTI with haematuria |
- Retest urine after treatment
- If persistent, investigate underlying cause
|
| Pregnancy |
- Send culture before antibiotics
- Nitrofurantoin 100mg MR bd for 7d (avoid at term)
- Treat asymptomatic bacteriuria
|
| Recurrent UTI |
- Send culture before antibiotics
- Hygiene/behavioral advice
- Consider urology referral
|
Complications
Renal
- Pyelonephritis
- Renal impairment/failure
- Renal/perirenal abscess
Systemic
- Sepsis
- Urinary stones
- Prostatitis (men)
Pregnancy
- Preterm delivery
- Low birth weight