For diseases that travel through the air, like COVID-19, special hospital rooms are essential for controlling pathogens and making sure they stay contained to one patient's room, rather than infecting others nearby (as happened with COVID-19 on cruise ships). They're called "airborne infection isolation rooms," or negative pressure rooms. You've probably read about them in stories about hospitals treating acute cases. They create a crucial barrier between extremely infectious people and everyone else.

But how do they work exactly? And why aren't they everywhere? To find out, we talked to Andrew Streifel, a hospital environment specialist who helped pioneer the design of these rooms in the 1980s, while trying to protect immunocompromised bone marrow transplant patients at the University of Minnesota Medical Center. He also contributed to the American Institute of Architects' guidelines of hospital design published in 1996. Streifel has penned numerous papers, and visited roughly 400 hospitals around the globe, consulting on the design and implementation of isolation rooms over his more than 40-year career. Even though he's retired, Streifel still consults, and his paper on converting stock hospital and hotel rooms into airborne infection isolation rooms is being referenced by healthcare providers around the world in response to the COVID-19 pandemic.

WHAT ARE NEGATIVE PRESSURE ROOMS?

The goal of a negative pressure room is simple. If someone is exhaling a virus or other contagion into the air, "you create a vacuum—a rather low-[pressure] vacuum," Streifel says. "You have to suck out more air than you are blowing in."