HAI (Hospital-acquired infection) is very common in ICU，and lack of understanding of environmental exposure omics and environment-host microbial interactions restricts the prevention and control of HAI. In this project, the investigators try to analyze the spatial and temporal distribution characteristics and evolution of microorganisms and their functions in the ICU environment through metagenome.

This observational study aims to analyze the spatial and temporal distribution characteristics and evolution of microorganisms and their functions in the ICU environment. The investigators will conduct weekly air microbiome sampling and microbiome sampling at 5 high-frequency contact points in different types of ICU units in three hospitals for one consecutive year, and collect dynamic pharyngeal swabs from ICU ward health care workers and dynamic clinical specimens (endotracheal aspiration, and bronchoalveolar lavage fluid) from patients with ventilator-associated pneumonia in ICU ward. With DNA high-throughput sequencing technology, the investigators will analyze the spatial and temporal distribution characteristics and evolution of microorganisms and their functions in the ICU environment, and provide support for HAI prevention.

Inclusion Criteria:

• With mechanical ventilation
• Age ≥18 years
• Anticipated ICU stay for more than 2 days
• With two or more of the following ventilator-associated pneumonia (VAP) risk factors
• VAP risk factors: Age ≥ 60 years old; Patients with chronic lung disease; Long-term bedridden; Unconsciousness; Sputum is not easily coughed up; Antibiotics have been used before mechanical ventilation; Long-term use of H receptor blockers and proton pump inhibitors.

Exclusion Criteria:

• Patients who have not signed the informed consent
• Pregnant
• Systemic diseases and recent use of related drugs
• History of infectious diseases, such as tuberculosis or PPD positive
• History of hypertension and poor blood pressure control (SBP / DBP > = 140mmHg)
• With severe mental illness
• Long term use of traditional Chinese medicine, probiotics, gastric mucosal protective agents, proton pump inhibitors, chemotherapy or immunosuppressive drugs, etc.

Patients with mechanical ventilation, age ≥18 years, anticipated ICU stay for more than 2 days, and with two or more of the following ventilator-associated pneumonia (VAP) risk factors were included in this study.