Would you assume their was no risk if one of your friends from Liberia just came back from a visit to Liberia and had a temp of 103 + and were throwing up and in severe pain?
"Half full or half empty doesn't matter. What matters is, you've only got half a glass...so what are you going to do about it?" - Me
He was exhibiting symptoms, had been to Liberia and sought professional care, initially they simply gave him anti-biotics and painkillers and sent him on his way, in that process if they didnt think he had Ebola during the initial assessment it's very likely they would have been careless.
It is very infectious in the sense that if you come into direct contact with someones symptoms you can get it if you're careless, like touching your face after dealing with someone.
It's most likely someone from the initial time he sought help.
Need to figure out if the nurse was exposed on Duncan's initial visit or during the treatment. If its the latter, the current consensus on the manner in which this disease can spread may be incorrect.