OBJECTIVE To explore the correlation between bacteria in ventilator circuits and time of lower respiratory tract infections so as to provide guidance for prevention of ventilator-associated pneumonia(VAP).METHODS A total of 122 patients with typeⅡ respiratory failure who were hospitalized for mechanical ventilation in the intensive care unit(ICU)from Jun 2015 to Jun 2016 were enrolled in the study.The specimens were collected from lower respiratory tract secretions,humidifier,condensation water collectors o...