Pathology

Most causative microorganisms are migratory bowel gut bacteria from the perineum, with Escherischia coli being the most common (in 80%). Other organisms include Proteus mirabilis, Staphylococcus epidermis and Streptococcus faecalis. Culture of infected urine characteristically produces a monoclonal growth; multiclonal growth may indicate a contaminated sample.

Women are much more commonly affected than men; they have a shorter urethra than men (Fig. 3.36.1) and this, and its position, makes contamination with bowel organisms more likely. Consequently, females should only be investigated if they have recurrent lower infections (> 3/year) while a single infection in a male should be investigated further. Other causes are:

urinary catheter: this may introduce organisms into the bladder; the risk increases if a long-term catheter is necessary

immunosuppression, e.g. diabetes

chlamydial infection: a sexually transmitted UTI

bladder outflow obstruction, e.g. kidney stones or benign prostatic hyperplasia

structural abnormalities: including posterior urethral valves, causing bladder outflow obstruction, or vesicoureteric reflux.

Fig. 3.36.1 The female urethra is 4 cm long (A); the male urethra is 18 cm long (B).