It has a specially designed air-flow system to prevent contaminated air from leaving the patient room. It requires anyone who enters to be buzzed in. Personnel who work there receive special training in infection control to prevent the spread of bio­terror agents, natural or man-made. It also has a tiny gym.

Welcome to the Special Clinical Studies Unit at the National Institutes of Health in Bethesda, Md. It is a 4,000-square-foot unit inside the NIH Clinical Center, the nation’s only hospital dedicated to research, which provides free state-of-the-art care to very sick patients from all over the world.

Now it’s home to its first confirmed Ebola patient, Nina Pham.

Pham is the first patient with a confirmed infectious disease to be cared for in the special seven-bed unit, center director John Gallin said in an interview Friday. Opened in 2010 for patients who need advanced isolation and extended stays, the unit was initially designed to take care of personnel working at the U.S. Army Medical Research Institute of Infectious Diseases in case they were exposed to infectious agents. In more recent years, it has been used to house healthy volunteers participating in live vaccine trials. The volunteers need to be monitored in a place where they can be safely quarantined, Gallin said. To accommodate those healthy volunteers, the unit has a dining room and a “tiny fitness area,” he said.

Pham, the first nurse diagnosed with Ebola after caring for a patient in Dallas, is in fair and stable condition, officials said Friday morning.

“We are giving her the best possible care on a symptomatic and systemic basis,” Anthony Fauci, director of NIH’s National Institute of Allergy and Infectious Diseases, said during a news conference.

Pham, 26, was transferred to the facility, one of four in the country with a special bio­containment unit, late Thursday. She was diagnosed with Ebola on Sunday, becoming the first person to contract the disease on U.S. soil. Pham had been part of the team that treated Thomas Eric Duncan, a Liberian man who flew to Dallas last month before being diagnosed with Ebola. Duncan died last week, four days before it was announced that Pham had contracted the disease.

“There is no specific therapy that has been proven to be effective against Ebola, and that’s why excellent medical care is critical,” Fauci said. He said Pham was “very, very tired” from her trip.

Patients infected with the Ebola virus require a large number of staffers to provide care around-the-clock. At NIH, that comes out to about 27 people a week — doctors, nurses, support staff — for one patient, Gallin said. With about 50 to 60 such personnel specially trained for infectious disease and critical care, NIH can only care for two Ebola patients at a time, he said.

The four facilities that provide such care were designed in the aftermath of the Sept. 11, 2001, terrorist attacks to protect against bio­terrorism. Two of them, Emory University Hospital in Atlanta and the Nebraska Medical Center, are each treating one Ebola patient. The other facility is St. Patrick Hospital in Missoula, Mont.

They require staff to undergo more rigorous training in infection control, and staff must follow strict protocol for putting on and taking off personal protective equipment in a separate anteroom. Officials say meticulous attention to detail in following protocols is what sets them apart from other facilities.

Emory has treated three Ebola patients, all of whom have recovered. The University of Nebraska treated one patient who recovered and is now caring for a freelance NBC cameraman. St. Patrick has not yet treated an Ebola patient. The hospital has received so many inquiries that it has set up a special hotline where they are transcribed and forwarded to the appropriate departments.

Unlike the Dallas hospital where Pham and another nurse were infected, which officials said most likely occurred because of a breach of protocol involving personal protective equipment, no health workers taking care of the Ebola patients at the special facilities have become infected.

“There is a step-by-step, checklisted procedure to putting on your personal protective equipment for when you go in to the patient’s room to perform your duties and when you come out,” said Mark Rupp, medical director of Nebraska Medical Center’s infection control department, which includes the special unit. “That’s the big difference with what goes on in our unit and what goes on in a regular intensive-care unit.”

The facilities have one person whose only job is to make sure health-care workers put on and take off their protective equipment correctly. At NIH, this person is dubbed “the Watsan,” Gallin said, because it sounds like the sidekick to Sherlock Holmes.

The Watsan “has the authority to stop everything at any moment if someone looks like they’re breaking protocol,” Gallin said. The Watson has a checklist, like a pilot’s preflight checklist, and everything has to be done in that order. If not, the Watson can “scream at them and tell them to stop,” Gallin said, which apparently happened at least once Thursday night when doctors and staff were admitting Pham.

The protective gear that health-care workers take off is autoclaved (sanitized via pressurized steam) and then incinerated. Equipment that is not disposable is disinfected according to the manufacturer’s directions. The units also have negative air pressure to prevent germs from spreading beyond patient rooms. For Ebola patients, contaminated air is not such a concern because the disease is not transmitted through the air, but through contact with bodily fluids.

Alice Crites and Mark Berman contributed to this report.