What illnesses need a negative pressure room?

Illnesses that need a negative pressure room are primarily airborne infectious diseases that spread through small airborne particles that can float in the air for long periods and travel beyond close contact. The most common illnesses that require negative pressure isolation, also called airborne infection isolation rooms, include tuberculosis, which is the classic example because TB bacteria can remain airborne for hours. Other illnesses include measles, which is highly contagious airborne, chickenpox and disseminated shingles caused by varicella zoster virus, and in certain situations, COVID-19, especially during aerosol-generating procedures like intubation, though COVID is primarily droplet and airborne. During outbreaks, illnesses like SARS, MERS, Ebola in some contexts, and avian influenza may require negative pressure rooms. The purpose of a negative pressure room is to keep air pressure lower inside the room than in the hallway, so air flows into the room and not out, preventing contaminated air from escaping and infecting others, while exhaust air is filtered through HEPA filters. Hospitals have special units for these patients with 6 to 12 air changes per hour, sealed doors, and monitoring. Negative pressure is not needed for standard droplet infections like flu or common cold that require only masks and regular rooms.