Background  Definitions Bacteriuria: bacteria in urine. May or may not be symptomatic. Significant bacteriuria: ≥10 5  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...