Negative air pressure is used to prevent the escape of microbes from rooms housing patients with airborne infections (e.g., TB, measles). Which statement best describes this purpose?

• A. It prevents microbes from entering the room
• B. It prevents microbes from exiting the room
• C. It sterilizes the air inside the room
• D. It eliminates odors from the room

Answer: (B)

Negative pressure creates a room environment where the room’s air pressure is lower than the surrounding areas. Because of this, air flows into the room when doors are opened, and contaminated air is exhausted away through a dedicated ventilation system (often filtered). This directional airflow contains airborne pathogens inside the room, preventing them from escaping to other parts of the facility and protecting others. It isn’t about sterilizing the air, eliminating odors, or preventing entry into the room; the main purpose is to keep infectious microbes from leaving the room.