Study Population and data collection. During 9 months period (January to September 2003) of study all patients on mechanical ventilation for more than 48 hours by endotracheal tube or tracheostomy were evaluated for the development of VAP. Data pertaining to the clinical suspicion of pneumonia included daily temperature, total leucocytes counts, PaO2 / FiO2 ratio, nature of tracheobronchial secretions, and chest X-ray. Each patient was assigned a score based on the simplified clinical pulmonary infection score (CPIS) criteria (23). Total points in this composite score vary from 1 to 10 points. Only those patients with a CPIS score of 6 or more were included in the study.