• Bacteriuria = the presence of bacteria in the urine
• Significant bacteriuria = >10⁵ colony forming units per ml of urine
• Commonest organisms involved are
  • E. coli (80%)
  • Proteus mirabilis
  • Pseudomonas aeruginosa
  • Streptococcus faecalis

Pathogenesis

• Urine proximal to the distal urethra is normally sterile
• Most UTIs are due organisms arising from faecal flora
• They are invariably the result of ascending infection
• Rarely urinary tract infections can arise secondary to bacteraemia
• Host defences against infection include:
  • Voiding of urine
  • Urinary antibodies
  • Desquamation of epithelial surfaces
  • Antibacterial enzymes - lactoferrin and lysozyme
  • Secretory urinary IgA
• UTIs can be uncomplicated or complicated
• Uncomplicated UTIs have no underlying structural abnormality
• Complicated UTIs arise secondary to a structural lesion and can result in renal damage

Investigation

• All upper UTIs require investigation
• Lower UTIs in children and men should be investigated
• The aims of investigation are to:
  • Establish the diagnosis of a UTI
  • Identify the organism involved and its antibiotic sensitivity
  • Exclude a structural or pathological abnormality of the urinary tract
• The diagnosis of a UTI can be suggested by dip-stick testing of urine
• The presence of nitrites or leucocyte esterase is very suggestive of a gram-negative infection
• Diagnosis can be confirmed by microscopy and culture of a MSU
• Investigation of the urinary tract in adults may involve ultrasound, IVU and cystoscopy

Lower urinary tract infection

• Symptoms include suprapubic pain, frequency and dysuria
• Treat with increased fluid intake and antibiotics
• Symptoms can be improved by alkalisation of the urine
• MSU should be repeated at 7 days to check that the infection has been cleared

Acute pyelonephritis

• Presents with pyrexia, frequency, dysuria and loin pain
• MSU will be positive for the infecting organism
• Imaging in the acute situation is not required
• Treatment is by parenteral antibiotics
• Complications included:
• Pyonephrosis - occurs if coexisting upper tract obstruction
• Required urgent decompression usually by percutaneous nephrostomy
• If inadequately treated can result in a perinephric abscess

Urinary tract infection in men

• Men are less susceptible to UTIs
• Infection is usually the result of bladder outflow obstruction
• Residual urine acts a nidus of infection
• A proven UTI in man required US, urinary flow rates and possible cystoscopy

Urinary tract infection in children

• 1% of boys and 3% of girls develop a UTI
• Risk factors include posterior urethral valves, neuropathic bladder and stones
• UTIs in childhood are associated with vesico-ureteric reflux
• Reflux of infected urine can result in scarring, hypertension and renal failure
• Scarring in the presence of sterile reflux is uncommon
• 30% of children with UTIs have VUR
• 50% of children with UTIs and VUR have renal scarring
• Most renal scarring occurs in the first two years of life
• Aims of treatment in children are to:
  • Relieve symptoms
  • Prevent recurrence
  • Identify predisposing factors
  • Prevent renal damage
• All neonates and boys require investigation after one infection
• Investigations will include US, IVU and possibly micturating cystogram
• Prophylactic antibiotics may be required for recurrent infections

Vesico-ureteric reflux

• Spontaneous resolution occurs in 80% of patients
• Indications for surgical reimplantation of the ureters are:
  • Recurrent UTIs resulting from poor compliance with antibiotic prophylaxis
  • Breakthrough infections with prophylaxis
  • Gross VUR with atonic ureters
• Alternatives to surgery includes subendothelial injection of collagen or Teflon at VUJ