An impoant factor for chronic pyelonerphritis is ?

Ans is 'b' i.e., Vesico-Ureteral refluxAll factors mentioned as options play an impoant role in the genesis of Chronic Pyelonephritis.However, if asked to choose one, I will go with Vesico-Ureteral Reflux."Although obstruction is an impoant predisposing factor in the pathogenesis of ascending infection, it is the incompetence of the vesico-ureteral valve that allows bacteria to ascend the crater into the pelvis"- Robbins 6th / 973 Obstruction and catheterization will both contribute to infection in the region of urethra & bladder. These form source of infection into the the pelvis but "in the absence of vesico-ureteral reflux, infection would remain confined to the bladder". Thus majority of patients without VUR suffer from urethritis and cystitis but not pyelonephritis.