New York City's public hospital system has been slipping 'plain-clothes patients' into emergency rooms to see how quickly the proper Ebola response is triggered.

They are paid actors or other staff members, and no one in the ERs — including supervisors —  knows who they are or when they're showing up. Chief Medical Officer Dr. Ross Wilson says the simulated patients only appear mildly ill, and it's up to the front-line staff to ask the right questions and jump into action.

"If those patients have symptoms and a travel history we would expect them to be isolated within a few minutes in that emergency room," Wilson said, "and then we would call the Department of Health and complete a further work-up with the patient being isolated."

Wilson said the drills are sharpening ER reflexes and pinpointing problems. One thing supervisors have noticed is that some staffers put on their protective suits correctly but then take them off incorrectly — something that could expose them to the virus in a real-world situation.

Wilson is hopeful drills like these reduce the chances of miscommunication, like the one that led a Dallas hospital to discharge a man who apparently told nurses he had traveled to Liberia.

"We're trying to minimize the risk. We hopefully are able to manage it," Wilson said. "But this is a very difficult process in a high volume and sometimes very active environment."

All eleven city hospitals have undergone the drill over the last month, and about half of them have done a second round.

A spokesman for the Greater New York Hospital Association said several facilities are undergoing similar drills.