Inclusion Criteria:  Recent cough, expectoration or aggravation of original respiratory diseases, with or without purulent sputum / chest pain / dyspnea / hemoptysis Fever Signs of pulmonary consolidation and / or moist rales Peripheral blood leukocytes >10×10^9/L or less than 4×10^9/L, with or without nucleus shifting to the left. New patchy infiltration, consolidation of lobes / segments, ground glass opacity or interstitial changes, with or without pleural effusion on chest imagings Positive etiological examination Age > 18 years old Need mechanical ventilation; septic shock need vasoactive drug treatment. Meet one of them. ① respiratory rate ≥ 30 beats / min; ② oxygenation index (PaO2 / FiO2) ≤ 250; ③ multilobar infiltration; ④ disturbance of consciousness / disorientation; ⑤ azotemia (BUN ≥ 20mg / dl); ⑥ cytopenia (WBC < 4.0 × 109 / L); ⑦ thrombocytopenia (platelet < 10.0 × 109 / L); Ⅷ low body temperature (T < 36 ℃); Ⅸ hypotension, requiring strong fluid resuscitation. Meet the above three requirements at the same time.  Exclusion Criteria:  ● Cannot understand and / or implement the investigation protocol.