From 2003 when Severe Acute Respiratory Syndromes (SARS) appeared，many new types of respiratory viruses emerge in endlessly. Therefore, the epidemiology and the clinical character has changed quietly, especially severe pneumonia. This cohort study aim to obtain the contents of severe pneumonia patients in Respiratory Intensive Care Unit (RICU). Through the clinical data analysis, the investigators could get the information of the pneumonia caused by different reasons, such as morbidity and mortality, risk factors, clinical symptoms and radiographic changes, the respiratory support parameter and so on. The investigators hope the result could guide them do the clinical work of severe pneumonia better in the future.