The purpose of this observational study is to collect prospective data on the occurrence of bacterial and viral pneumonia in the ICU setting. Current classification systems for pneumonia promote over treatment with antibiotics as they do not specifically recognize the presence of culture-negative and viral pneumonia. The investigators will collect data to determine if a novel pneumonia classification system can be developed that more accurately links the etiology of pneumonia (antibiotic-susceptible bacterial pneumonia, antibiotic-resistant bacterial pneumonia, culture-negative pneumonia, viral pneumonia) to clinical outcomes. Additionally, the investigators will collect data on the practice of antimicrobial stewardship in the ICU setting to determine if further improvements in antibiotic practices can be accomplished in the future.