Inclusion Criteria:  Patients who receive abdominal operations with routinely abdominal drainage placement.  Abdominal infection is suspected by the clinicians, and one of the following conditions is met:  Temperature ≥38℃; One of the following laboratory indicators: WBC≥10×10^9/L, PCT≥0.5ng/ml, hsCRP≥100mg/L.  Exclusion Criteria:  Patients who are diagnosed with the abdominal infection before surgery. Evidence of non-abdominal infection is clear and could explain the clinical symptoms.