Nosocomial pneumonia refers to pneumonia caused by pathogens in the lower respiratory tract of the elderly under special circumstances. This infection does not exist when the patient is admitted to the hospital, nor is it in the latent period of infection. Instead, it occurs in the hospital (including nursing homes for the elderly and rehabilitation homes) 48 hours after hospitalization. However, it also includes patients who are infected during hospitalization and develop the disease after discharge. Therefore, other pulmonary infectious diseases that are latent during this period should be excluded. Hospital-acquired pulmonary infection is an important area of great concern in clinical medicine, preventive medicine, hygiene and hospital management in recent years. All countries have invested a lot of manpower, material resources and financial resources to conduct in-depth and detailed research. This disease not only poses a huge threat to human life and safety, but also causes huge losses to social wealth.