 The multi-center study was conducted in four academic teaching hospitals in Tehran, Iran. The study consisted of a 3-month baseline observation period October 2011-December 2011, Period 1, followed by a 6-month intervention period January 2012 to June 2012 and a 3 July 2012-September 2012, Period 2, 15 October 2012-December 2013, Period 3 and 21-months January 2014-June 2015, Period 4 follow-up periods. The protocol for Evidence based guidelines EBGs for preventing VAP remained unchanged throughout the study period in every ICU. 