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Objective: To understand the internal circuit contamination of ventilator in mechanical ventilation patients, to evaluate the effect of ventilator internal circuit disinfection and the impact on the incidence of ventilator-associated pneumonia (VAP)., Methods: A total of 39 patients with mechanical ventilation admitted to intensive care unit (ICU) of Hangzhou Geriatric Hospital from January 2017 to June 2018 were enrolled. Routine mechanical ventilation treatments for patients included pipeline replacement, aseptic operation, prevention of infection, etc. After 2 weeks of mechanical ventilation, the internal circuit of the ventilator was disinfected using the internal circuit sterilizer of the ventilator. Microorganism sampling and detection at 3 cm to the exhalation port of the internal circuit of the ventilator was performed before and after disinfection. The number of colonies was < 5 cfu/cm 2 and no pathogenic bacteria could be detected. During the observation period, if the patient was complicated by VAP for anti-infective treatment, the ventilator with internal loop disinfection was replaced after infection control, and was incorporated again into the group for observation. The number of microbial colonies in the internal circuit of the ventilator before and after disinfection, the microbiological test pass rate and the incidences of VAP during the 2 weeks were observed., Results: All 39 patients were included in the analysis, with 23 male and 16 female; with age of 65-97 years old, average (78.7±7.6) years old. Before the disinfection, 9 604 strains were detected in the internal circuit of the ventilator, including 8 687 strains of Gram-negative bacilli (90.4%), 902 strains of Gram-positive cocci (9.4%), and 15 strains of fungi (0.2%), which were detected in the lower respiratory tract of the patients. The strain concordance rate was 41%. The qualified rate of microbial detection in the internal circuit of the ventilator was 5.1%; 13 cases (33.3%) of VAP occurred during 2 weeks of mechanical ventilation. After disinfection, 785 strains of pathogens were detected in the internal circuit of the ventilator, and the number of colonies was significantly reduced compared with that before disinfection [cfu/cm 2 : 0 (0, 20) vs. 150 (15, 500), P < 0.01], of which 688 strains of Gram-negative bacilli (87.7%), 92 strains of Gram-positive cocci (11.7%) and 5 strains of fungi (0.6%) were found; the qualified rate of microbial detection in the internal circuit of ventilator reached 71.8%, which was significantly higher than that before disinfection (P < 0.01); 2 weeks after mechanical ventilation the incidence of VAP decreased slightly during the period [20.5% (8/39) vs. 33.3% (13/39)], but there was no significant difference (P > 0.05)., Conclusions: The internal circuit of the ventilator can be used to detect the pathogen and the sputum culture of the patients on mechanical ventilation with a high consistency. The disinfection of the pathogen could significantly reduce the air pollution of the ventilator and reduce the occurrence of VAP in the patients.