Urinary tract infection (UTI)

• Background 

  

  Definitions

  • Bacteriuria: bacteria in urine. May or may not be symptomatic.
  • Significant bacteriuria: ≥105 colony forming units (CFU)/ml in mid-stream urine (MSU).
  • UTI: significant bacteriuria + symptoms.
  • Complicated UTI: UTI in the presence of certain risk factors, including renal or urinary tract abnormality, voiding difficulty, ↓kidney function, indwelling catheter, immunosuppression, or virulent organism (e.g. Staph. aureus).
  • Recurrent UTI: reinfection (new organism) or relapse by same organism (usually within 2 weeks). No strict definition, but 2-3 per year is a common one.
  • Abacterial cystitis: symptoms without bacteria. Sometimes occurs in women.

  Pathogens

  • E. coli (90%).
  • Staph. saprophyticus: occurs in sexually active women.
  • Proteus mirabilis: suggests kidney stones.
  • Enterococcus faecalis: causes prostatitis.
  • Klebsiella: usually in catheterised patients.
  • Staph. aureus: from hematogenous spread.
  • STIs: chlamydia, gonorrhea.

  Epidemiology

  • Annual incidence: 1/10 women, 1/100 men.
  • Lifetime risk: 1/2 women, 1/20 men.
  • Risk increases with age.
  • Although less common in men, they account for 40% of UTI hospitalizations.

• Signs and symptoms

  Symptoms:

  • Cystitis (lower UTI): frequency, urgency, dysuria, nocturia, haematuria, suprapubic ache.
  • Acute pyelonephritis (upper UTI): fever ± rigors, loin pain, systemically unwell (e.g. vomiting).
  • Prostatitis and urethritis are technically UTIs, but are often considered separately. Prostatitis may present flu-like, with low backache, but few urinary symptoms. See also STIs causing urethritis.

  Signs:

  • Fever
  • Suprapubic or loin tenderness.
  • Cloudy or smelly urine.
  • Swollen, boggy, tender prostate (prostatitis).
  • Discharge (STI urethritis).

• Risk factors

  • Demographic: female, age.
  • Pregnancy
  • Pathogen exposure: sexually active, catheter.
  • Stagnant flow: obstruction (prostate, stones), retention, extended holding.
  • Infection-prone states: diabetes, immunosuppression.

• Differential diagnosis

  • Overactive bladder.
  • STIs
  • Non-infectious inflammation: atrophic vaginitis, interstitial cystitis, Reiter's syndrome, drug-induced cystitis (cyclophosphamide, allopurinol, danazol, ketamine) or urethritis (NSAIDs).
  • Vaginitis
  • Stones
  • Bladder or renal cancer.

  Most can be excluded with urine dipstick.

• Investigations

  Urine dipstick:

  • Nitrites or leukocyte esterase +ve.
  • Sensitivity: 90% in GP and emergency department, 80% in inpatients. Specificity: 80%; nitrites are more specific than leukocytes.
  • If +ve: start treatment and send MSU for microscopy, culture, and sensitivity (MC+S). MSU optional in uncomplicated first UTI in women.
  • If -ve: send MSU anyway if strong clinical suspicion, male, child, pregnant, or immunosuppressed.

  MSU MC+S:

  • Microscopy shows leukocytes ± bacteria.
  • If <105 CFU/ml but pyuria (>20 WBC/mm3), known as 'sterile pyuria'. Causes include a previously treated UTI, prostatitis, STI, TB, appendicitis, bladder tumour, stones, polycystic kidney disease, or drug-induced cystitis.
  • If many different organisms, suspect contaminated sample (i.e. not mid-stream) and repeat MSU.

  Further investigations if indicated:

  • Pyelonephritis: FBC, U+E, CRP, blood cultures. Imaging may help identify predisposing factors, especially CT.
  • Blood glucose to rule out diabetes.
  • Imaging: kidney US (obstruction/hydronephrosis), post-void bladder US, CT KUB (stones).

• Management

  General approach:

  • Antibiotics if symptomatic.
  • Paracetamol +/or NSAIDs for symptom relief.
  • Remove catheter if present.

  Lower UTI

  Women

  Single UTI:

  • Nitrofurantoin (if eGFR ≥45) or trimethoprim PO 3 days.
  • Pregnancy: treat even if asymptomatic. Nitrofurantoin 1st line (unless at term), amoxicillin or cefalexin 2nd line, all PO for 7 days.
  • Any other complicated UTI (e.g. abnormal renal tract, immunosuppressed, uncontrolled diabetes, catheter-associated): trimethoprim or nitrofurantoin PO 7 days.

  Preventing recurrent UTI:

  • Behavioural and lifestyle: increase daily water intake, pre/post-coital washing, avoid spermicides and diaphragm. Evidence is limited for cranberry juice and pre/post-coital voiding.
  • Consider vaginal estrogen if postmenopausal.
  • Prophylactic antibiotics if very disruptive: nitrofurantoin (if eGFR ≥45) or trimethoprim PO, taken postcoitus if sex-related, otherwise daily.

  Urology referral and imaging indications:

  • Failure of above measures.
  • Has risk factors for urinary tract abnormality: obstructive symptoms, history of stones, urinary tract surgery, gynae cancer.
  • Immunosuppressed
  • Recurrent UTI with haematuria: urgent referral for suspected cancer.

  Men

  • Nitrofurantoin (if eGFR ≥45) or trimethoprim PO 7 days for cystitis.
  • Ciprofloxacin PO 2-4 weeks if there is prostatitis, IV if severely unwell.
  • Urology referral and imaging indications: treatment failure, underlying risk factor (e.g. obstruction), upper UTI, recurrent UTI (2 in 3 months) including urgent referral if associated with haematuria (possible cancer).

  Upper UTI

  • Most upper UTIs are uncomplicated and can be managed with PO antibiotics e.g. cefalexin or ciprofloxacin 7-10 days.
  • If there is no response within 24 hrs, signs of sepsis, or in complicated UTI → hospitalisation and consider IV antibiotics e.g. 2nd-3rd generation cephalosporin or ciprofloxacin.

• Complications and prognosis

  • Infectious spread: pyelonephritis, perinephric or intrarenal abscess, prostatitis, sepsis.
  • Kidney: AKI, hydronephrosis.
  • Recurrence: 1 in 3 women, usually reinfection (new pathogen).
  • Prognosis: symptoms resolve in 3-4 days with an effective antibiotic, vs. 5-7 days without treatment (or with a resistant organism).