There is a huge difference between being in a room with someone with early stages of ebola for a few minutes and working in a hospital. Here are some factors when working in a hospital with ebola patients; 1. Much longer contact periods. Many health workers in Africa work 18 hour days. 2. Much closer contact. Health workers touch ebola patients much more often than the general public. 3. Contact later in the disease progression. Ebola is transmitted by bodily fluids. As the disease progresses more bodily fluids are secreted, it is a hemorrhagic disease, and more pathogen is present in the excretions.
If one works long hours and their suit is covered in ebola laden fluids it is quite probable that a small mistake can cause infection. Even the fatigue factor may cause errors in protocol.
The nurses in Texas who contracted Ebola from Duncan, do you believe that they had "prolonged" contact with him?
The Ebola virus spreads through bodily fluids including saliva (aerosolized when sneezing) and sweat. I think it is easier to spread than is currently believed, especially because fluids are more readily spread than is understood even by health experts.
Also, the Ebola virus apparently can live outside the body for several days if encapsulated in body fluids.
Anyone can verify these facts about about Ebola on the US CDC FAQ about Ebola.