An application for a PEEP valve includes a filter media in the air flow between a patient interface and exit vent(s). The patient interface is connected to a patient airway system and the exit vents exhaust exhalation gasses into the atmosphere. The filter prevents or reduces the passage of microbes from the patient's exhalation gasses into the atmosphere. The PEEP valve provides positive gas pressure to a patient's lungs, requiring a predetermined exhalation gas pressure to be exceeded before releasing exhalation gasses into the atmosphere.