Corticosteroid Therapy for Severe Community-Acquired Pneumonia

Inclusion Criteria: * community-acquired pneumonia * PSI score：4-5 * with at least one of following conditions：①CRP ≥150 mg/L,②oxygen index ≤250 , ③bilateral or multi-lober infiltrates in chest image,④ area of pulmonary infiltrates increase \>50% with 48 hous,⑤fever higher than 39℃ exceed 72 hours Exclusion Criteria: * nosocomial Pneumonia * aspiration pneumonia * acute burn injury * gastrointestinal bleeding within the past three months * uncontrolled diabetes mellitus * pregnant or breast feeding * a condition requiring treatment with greater than 0.5 mg/kg/d of prednison or its equivalent * severe immunosuppression (human immunodeficiency virus infection, immunosuppressive conditions or medications) * active tuberculosis * preexisting medical condition with a life expectancy of less than 3 months