Hospital-acquired infections can also be referred to as in-hospital infections, nosocomial infections or hospital-acquired infections. China unified the definition of hospital-acquired infections in 2001, which mainly refers to infections acquired by hospitalized patients in the hospital, including infections that occur during hospitalization and infections acquired in the hospital and occurring again after discharge, but not including infections that have started before admission or existed at the time of admission. Infections acquired in the hospital by hospital staff also belong to hospital infections. It can be divided into exogenous infection and endogenous infection. Exogenous infection, also known as cross-infection, refers to the infection caused by patients, staff and visitors in the hospital carrying pathogens, as well as the infestation or customization of bacteria in the hospital environment, and endogenous infection, also known as self-infection, refers to the normal flora parasitized in the patient’s own skin, mouth, pharynx and gastrointestinal tract, due to the number or parasitization site of Infections caused by changes in the number or location of the parasites.