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.

The investigators will be prospectively collecting data on patients admitted to the 8300 and 8400 medical intensive care units at Barnes-Jewish Hospital requiring invasive mechanical ventilation for support in respiratory failure from pneumonia. Data will be collected on patients admitted from 1/2016-12/2016. The investigators will be collecting initial patient characteristic data as well as reviewing microbial specimen results (tracheal aspirate, bronchial alveolar lavage, viral multiplex, blood cultures) and antibiotic usage in real time. The investigators will identify any changes in antibiotic usage demonstrated with the advising of the ICU antibiotic stewardship team.

Inclusion Criteria:

• age 18+, admitted for 8300 or 8400 medical ICU between 1/2016 and 12/2016 for respiratory failure from pneumonia, requirement of > 24 hours of invasive mechanical ventilatory support for pneumonia

Exclusion Criteria:

• Immunocompromised as defined by HIV/AIDS, known immunodeficiency, chronic steroids > 20mg/day Prednisone equivalent, other home immunosuppressants, solid organ or bone marrow transplant patients, cystic fibrosis, bronchiectasis, active malignancy, receiving chemotherapy or radiation therapy within the past 3 months, hematologic malignancy
• Chronic ventilator dependence

Patients in the 8300 and 8400 medical intensive care units at Barnes-Jewish Hospital with respiratory failure from pneumonia requiring invasive mechanical ventilation.