Prophylaxis reduced the risk of recurrences by 50 % ( hazard ratio , 0.50 ; 95 % CI , 0.34 to 0.74 ) and was particularly effective in children whose index infection was febrile ( hazard ratio , 0.41 ; 95 % CI , 0.26 to 0.64 ) and in those with baseline bladder and bowel dysfunction ( hazard ratio , 0.21 ; 95 % CI , 0.08 to 0.58 ) .