Data management and quality control
The data entry clerks of each unit underwent uniform training before the start of the project and strictly followed the guidelines of the study protocol. EpiData software was applied to establish the database and the data of the case reports were entered after conducting consistency check by two doctors. Each participating unit collected data in real-time and uploaded relevant data after the infants were discharged from the hospital and the database was locked after verification and eliminating of errors. The technical staff of each unit kept close contact with the other participating unit at all times to check the case records, verify the accuracy of the data and solve any associated problems in a timely manner.