A negative pressure room is a type of hospital room designed to prevent airborne microorganisms in the room from entering hallways and corridors, and to prevent cross-contamination from room to room. It is called a negative pressure room because the air pressure inside the room is lower than the air pressure outside the room. This means that when the door to a negative pressure room is opened, non-contaminated filtered air will flow into the room while any harmful particles and/or potentially contaminated air located inside the room is sucked out with exhaust systems. Negative pressure rooms are used to isolate patients with contagious, airborne diseases such as measles, tuberculosis, SARS, MERS, and COVID-19. They are also used in medical facilities to prevent the spread of contagious illnesses from one area to another. Negative pressure is generated and maintained in a room by a ventilation system that continually attempts to move air out of the room. Replacement air is allowed into the room through a gap under the door, and the room is as airtight as possible, allowing little air in through cracks and gaps. Leakage from these sources can make it more difficult and less energy efficient to maintain room negative pressure.