A dichotomy of opinion exists regarding the incidence of infection after urinary instrumentation. Determinants of infection exist which explain these opposing viewpoints. That the condition of the urinary bladder is a major variable in the incidence of infection was demonstrated by a low incidence of retention catheter-induced infection in 80 patients with normal bladders. Further studies on the bladder indicated that the normal bladder is resistant to infection and that this resistance is a function of two bladder defense mechanisms: (1) voiding, and (2) intrinsic antibacterial activity.
Cox CE, Hinman F. Retention Catheterization and the Bladder Defense Mechanism. JAMA. 1965;191(3):171–174. doi:10.1001/jama.1965.03080030015003