Time of onset of pneumonia is an important epidemiologic variable, risk factor for specific pathogens, and outcomes in patients with HAP and VAP. Early onset HAP and VAP, defined as occurring within the first four days of hospitalization, usually carries a better prognosis and is more likely to be caused by antibiotic-sensitive bacteria. Late onset HAP and VAP (> 5 days) is more likely to be caused by multi-drug resistant (MDR) pathogens and is associated with increased patient mortality and morbidity. However, patients with early onset HAP that have received prior antibiotics or that have had prior hospitalization within the past 90 days are at greater risk for colonization and infection with MDR pathogens and should be treated similar to patients with late onset HAP or VAP (51). Since delays in the administration of appropriate therapy have been associated with excess hospital mortality from HAP (52-56), the prompt administration of empiric therapy for patients likely to have VAP is essential. Attributable mortality from HAP was significantly lower among patients receiving initial appropriate antibiotic treatment compared to patients requiring a treatment change (16.2% vs. 24.7%; p = 0.034) (57).