Final answer:
Invasive procedures are the major cause of UTIs in hospitalized patients, primarily due to urinary catheter use which can introduce bacteria into the urinary tract.
Step-by-step explanation:
The majority of urinary tract infections (UTIs) in hospitalized patients are caused by invasive procedures, such as the use of urinary catheters. These procedures can introduce bacteria into the urinary tract, creating an opportunity for infection. Other factors like inadequate perineal care and immunosuppression can also contribute to the development of UTIs, but invasive procedures are the primary cause in the hospital setting since they directly compromise the closed sterility of the urinary system.