Hospital-acquired infections are infections that occur in the hospital environment among patients or healthcare workers, including infections that occur during hospitalization and infections that are acquired in the hospital and show clinical manifestations after discharge. Its characteristics include the object of infection, the time of infection, and the people who are easy to be infected. 1. Objects of infection: The objects of infection are all active people in the hospital, such as inpatients, outpatients, visitors, escorts and hospital staff, but most of them are in the hospital, and the place of infection is in the hospital. 2. Time of infection: Infection usually occurs 48 hours after hospitalization or shortly after discharge from the hospital, and the time of infection is usually not less than 24 hours. 3. People susceptible to infection: Infected patients are usually old and weak, immunocompromised or suffering from various underlying diseases such as leukemia, diabetes, uremia, cirrhosis, heart disease and central nervous system diseases. Hospital-acquired infections can be associated with the application of certain therapeutic measures or medications, such as the application of high-dose antibiotics, interventional procedures, immunological agents and chemotherapeutic drugs.