Most often these infections are NOSOCOMIAL, meaning that they are hosptial acquired, due to prolonged ICU stay, use of multiple antibiotics including aminoglycosides / higher generation cephalosporins etc.
Other causes include foreign bodies, IV catheters, gut ulcers, liver diseases etc.
So ot answer your question while this is not a side-effect of surgery per se, it is the side-effect of prolonged hosptila stay as a result of any extensive surgery and use of antibiotics (which cannot be avoided).
Read more here
http://www.emedicine.com/MED/topic678.htm
regards
Dr. Gupta

