LEIGH SALES, PRESENTER: How did it happen? That's the question embarrassed health officials in the United States are asking themselves after a second nurse contracted the deadly Ebola virus after treating a patient.

What's even more disturbing is that the nurse travelled on a commercial flight despite having a temperature.

The case is causing growing concern about the competence of American authorities to prevent the spread of Ebola, as North America correspondent Ben Knight reports from Atlanta, where the sick nurse has been transferred.

BEN KNIGHT, REPORTER: Another rude awakening in America. HazMat teams swoop in at dawn to decontaminate the apartment of yet another Ebola victim.

26-year-old Amber Vinson is the second nurse caring for America's first Ebola patient to catch the virus herself.

A month ago, who would have thought it would come to this? Certainly not the US President.

BARACK OBAMA, US PRESIDENT (Sept. 16): In the unlikely event that someone with Ebola does reach our shores, we've taken new measures so that we're prepared here at home. ... We're working with hospitals to make sure that they are prepared.

BEN KNIGHT: But that patient did arrive, and immediately, the system fell apart, from the moment Thomas Duncan was sent home from a Dallas hospital with a packet of antibiotics, dying and contagious with Ebola.

Still, the US authorities were urging calm.

LISA MONACO, US HOMELAND SECURITY ADVISOR (Oct. 4): The United States is prepared to deal with this crisis, both at home and in the region. Every Ebola outbreak over the past 40 years has been stopped. We know how to do this and we will do it again.

GAVIN MCGREGOR-SKINNER, DEPT OF PUBLIC HEALTH SCIENCES: It's an example of being completely overconfident, telling the American public what they want to hear, but completely underestimating what's actually required.

BEN KNIGHT: Gavin McGregor-Skinner is an infectious diseases expert who's been advising African and US hospitals on how to prepare for Ebola.

GAVIN MCGREGOR-SKINNER: The US has no national communication plan for Ebola. And we've seen mixed messages, we've seen the confusion.

BEN KNIGHT: It's hard to point to anything that's gone right, especially at the hospital in Dallas.

Like the way Thomas Duncan was left to wait with other patients in the emergency room, instead of being immediately isolated. How, when he finally was admitted, the dozens of staff who cared for him didn't have the right protective gear, leaving their skin exposed to the worst known strain of Ebola virus in the world.

GAVIN MCGREGOR-SKINNER: These patients are really sick. They have projectile vomit. They have a lot of diarrhoea. They require intense patient care.

BEN KNIGHT: But worse than that, even if they had followed the instructions from the Centers for Disease Control to the letter, they wouldn't have been safe.

Gavin McGregor-Skinner says the CDC protocols, the ones the rest of the world looks to as the gold standard, are wrong.

GAVIN MCGREGOR-SKINNER: The face is exposed, the hair is exposed. Imagine if you followed the CDC protocol and a patient projectile vomited on you and you got vomit with billions of virus in your hair. I don't know as a biosafety expert how I'm going to decontaminate you and help you not get the disease.

BEN KNIGHT: Two of the nurses who treated Thomas Duncan in Dallas have now become infected with Ebola. 77 others are being monitored for symptoms.

Add to them more than a 130 passengers who shared a plane with Amber Vinson from Cleveland to Dallas the night before she was hospitalised with the virus.

DALLAS HEALTH OFFICIAL: I have activated our emergency command centre. I believe it has risen to that level.

We, um, are preparing contingencies for more and that is a very real possibility.

BEN KNIGHT: Health authorities in the US believed that any hospital in this country with an isolation room could deal with an Ebola case. But what happened in Dallas showed just how wrong they were.

And so now it's come to this: Amber Vinson has been taken out of Dallas and is now being brought here to the Emory Hospital in Atlanta in Georgia. When her ambulance gets inside and she enters this hospital she'll be entering a specialist facility, a hospital that's been specifically set up to deal with contagious and infectious diseases like Ebola. Now there are four of these facilities in the US and between them they have fewer than 20 beds. Now with nearly 200 people now potentially on the Ebola watch list, what happens when all of those beds are full?

BARACK OBAMA: If we are not responding internationally in an effective way and if we do not set up the kind of preparedness and training in our public health infrastructure here in the United States, not just for this outbreak, but for future outbreaks, then we could have problems.

GAVIN MCGREGOR-SKINNER: I think what we're seeing is through - from the President down, panic. And I heard the President say today, "We need to be more aggressive." No, we don't. We need to follow exactly the standards, the protocols, the procedures, the management, the supervision processes that we put in place in West Africa.

BEN KNIGHT: Americans are wondering why their country can't seem to achieve what can be done in tent hospitals in the developing world and they're deeply concerned about how far this will spread before their own health system catches up.

LEIGH SALES: Ben Knight reporting from Atlanta.