Urinary Tract Infection
Summary
Urinary tract infection (UTI) is one of the most common bacterial infections, affecting the bladder (cystitis) or kidneys (pyelonephritis). Escherichia coli accounts for 80% of cases. Uncomplicated cystitis in women can be treated empirically with a short course of nitrofurantoin or trimethoprim. Pyelonephritis requires longer treatment and may need hospitalisation if severe. Men with UTI always require investigation. Catheter-associated UTI is a major cause of hospital-acquired infection. Recurrent UTI may benefit from prophylaxis.
Key Facts
- Most Common Organism: E. coli (80%)
- Prevalence: 50-60% of women have ≥1 UTI in their lifetime
- Uncomplicated Cystitis (Women): Nitrofurantoin 100mg BD for 3 days
- Pyelonephritis: Ciprofloxacin 500mg BD for 7 days (or IV if sepsis)
- Men with UTI: Always investigate (prostate, renal tract)
- Pregnancy: Treat asymptomatic bacteriuria (prevents pyelonephritis)
Clinical Pearls
"Cystitis = Lower, Pyelonephritis = Upper": Dysuria/frequency without systemic symptoms = cystitis. Fever + loin pain = pyelonephritis.
"Pregnant Women Need Treatment for Asymptomatic Bacteriuria": Untreated asymptomatic bacteriuria → 30% develop pyelonephritis → preterm labour.
"Men with UTI Always Need Investigation": UTI in men is complicated by definition — investigate for prostate disease, renal stones.
Why This Matters Clinically
UTI is extremely common and usually straightforward to treat. However, missed pyelonephritis or urosepsis can be life-threatening. Antibiotic stewardship is important — short courses work for uncomplicated cystitis. Recurrent UTI significantly impacts quality of life.
Prevalence
| Group | Lifetime Risk |
|---|---|
| Women | 50-60% have ≥1 UTI |
| Men | 10-15% |
| Recurrence | 25-30% of women within 6 months |
Risk Factors
| Factor | Details |
|---|---|
| Female Sex | Short urethra |
| Sexual Activity | "Honeymoon cystitis" |
| Menopause | Loss of oestrogen → altered flora |
| Catheterisation | Major risk for CAUTI |
| Diabetes | Impaired immunity, glucosuria |
| Urological Abnormalities | Stones, strictures, BPH |
| Pregnancy | Ureteral dilation, stasis |
Mechanism
Ascending Infection:
- Periurethral colonisation
- Bacterial ascent through urethra
- Bladder colonisation (cystitis)
- May ascend to kidneys (pyelonephritis)
Virulence Factors (E. coli)
- Type 1 fimbriae (bladder adherence)
- P fimbriae (kidney adherence)
- Haemolysin (tissue damage)
- Capsule (immune evasion)
Organisms
| Organism | Frequency |
|---|---|
| E. coli | 80% |
| Staphylococcus saprophyticus | 10-15% (young women) |
| Klebsiella | 5% |
| Proteus | 5% (associated with stones) |
| Enterococcus | Less common |
| Pseudomonas | Catheter-associated |
Lower UTI (Cystitis)
Upper UTI (Pyelonephritis)
Red Flags
[!CAUTION] Red Flags:
- Urosepsis (fever, tachycardia, hypotension)
- Obstruction with infection (urgent decompression)
- Pregnancy with UTI
- Men with UTI (always investigate)
Abdominal
- Suprapubic tenderness (cystitis)
- Costovertebral angle tenderness (pyelonephritis)
- Abdominal mass (distended bladder if obstructed)
Vitals
- Fever (upper UTI)
- Tachycardia
- Hypotension (urosepsis)
| Test | Purpose |
|---|---|
| Urine Dipstick | Screening (nitrites, leucocytes) |
| MSU Culture | Gold standard; guides treatment |
| Bloods | FBC, U&E, CRP if systemic |
| Blood Cultures | If sepsis |
| Renal USS | Obstruction, stones, abscess |
Uncomplicated Cystitis (Women)
| Drug | Dose | Duration |
|---|---|---|
| Nitrofurantoin | 100mg BD (MR) | 3 days |
| Trimethoprim | 200mg BD | 3 days |
| Pivmecillinam | 400mg TDS | 3 days |
| Fosfomycin | 3g single dose | Once |
Pyelonephritis
| Severity | Treatment | Duration |
|---|---|---|
| Mild (outpatient) | Ciprofloxacin 500mg BD | 7 days |
| Moderate-Severe | IV antibiotics, then oral | 7-14 days |
Pregnancy
- Treat asymptomatic bacteriuria
- Nitrofurantoin or Cefalexin
- 7 days
| Complication | Notes |
|---|---|
| Pyelonephritis | Ascending from untreated cystitis |
| Urosepsis | Medical emergency |
| Renal Abscess | May need drainage |
| Preterm Labour | In untreated pregnancy UTI |
| Recurrence | Common; may need prophylaxis |
Response to Treatment
- Uncomplicated cystitis: 90% respond in 48 hours
- Pyelonephritis: Improvement in 48-72 hours
Recurrence
- 25-30% recur within 6 months
- Prophylaxis reduces recurrence by 80%
Key Guidelines
- NICE NG109: UTI in adults (2018)
Key Evidence
Cochrane Reviews:
- Short-course (3 days) vs long-course for uncomplicated cystitis — equally effective
- Cranberry products — insufficient evidence for treatment; may help prevention
What is a UTI?
A urinary tract infection (UTI) is a bacterial infection in your bladder or kidneys. It's very common, especially in women.
What are the symptoms?
Bladder infection:
- Burning when you pee
- Needing to pee frequently and urgently
- Pain in your lower tummy
Kidney infection:
- Fever, feeling unwell
- Pain in your back/side
- Nausea and vomiting
How is it treated?
- Antibiotics (usually 3 days for bladder infection)
- Drink plenty of fluids
- Pain relief if needed
When to see a doctor urgently
- Fever with back pain
- Blood in urine
- Feeling very unwell
- Pregnancy with UTI symptoms
Primary Guidelines
- National Institute for Health and Care Excellence. Urinary tract infection (lower): antimicrobial prescribing (NG109). 2018. nice.org.uk/guidance/ng109
Key Resources
- Public Health England: UTI management guidelines
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