Associated factors virulence and quantity Exotoxin. Endotoxin Defense mechanism Immunologic function, age, etc Chronical diseases Nephropathy, Liversclerosis, Connective tissue diseases, Diabetes mellitus, Malignant tumor, and so on Medical factors: long-term Steriods, Antibiotics, All kinds of instrumentation such as invasive meauver catheterizationvirulence and quantity Exotoxin, Endotoxin Defense mechanism Immunologic function,age,etc Chronical diseases： Nephropathy,Liver sclerosis,Connective tissue diseases,Diabetes mellitus,Malignant tumor,and so on Medical factors： long-term Steriods,Antibiotics,All kinds of instrumentation such as invasive meauver,catheterization Associated factors