This is a prospective and exploratory study, which utilizes non-targeted metagenomic next-generation sequencing (mNGS) detecting drain fluid from patients who are suspected of postoperative abdominal infection. This study aims to explore the clinical value of mNGS in the rapid diagnosis of postoperative abdominal infection, to refine the pathogenic bacteria spectrum, and to establish a novel procedure for postoperative abdominal infection diagnosis.

Inclusion Criteria:

1. Patients who receive abdominal operations with routinely abdominal drainage placement.

2. Abdominal infection is suspected by the clinicians, and one of the following conditions is met:

   1. Temperature ≥38℃;
   2. One of the following laboratory indicators: WBC≥10×10^9/L, PCT≥0.5ng/ml, hsCRP≥100mg/L.

Exclusion Criteria:

1. Patients who are diagnosed with the abdominal infection before surgery.
2. Evidence of non-abdominal infection is clear and could explain the clinical symptoms.

Patients receive abdominal surgery including pancreatic, gastrointestinal, biliary surgery, etc. with routinely placing abdominal drainage in Peking Union Medical College Hospital. They are clinically suspected with postoperative abdominal infection.