Duncan had diarrhea and vomiting the night before he went to the hospital and infected zero people in the apartment. It appears the only reason he infected two healthcare workers is CDC stupidity.
The problem with the author's numbers is that he gathers his statistics from a particularly stupid subset of the human population in W. Africa. These are the people who carry corpses around in taxis. They kiss the bodies. They hide their relatives who are dying of ebola from the authorities. None of those statistics apply here.
What does apply here is the fact that Obama is bringing 150 Ebola refugees here a day. That number is sure to increase. The number of infected refugees, currently roughly 1 in 1000 is also sure to increase. Each of the refugees brings a unique set of risks to America. None of them are a statistic. Some might be terrorists and a much greater threat. Most will just cost us $1m in municipal expenses plus $500k in hospital expenses not to mention the risk to hospital employees.
It's important to focus on the source of the problem: the influx of Ebola refugees who will kill actual Americans, not just statistical Americans.
Where are those people, and do we know that they are uninfected?
African diseases that will kill you: AIDS, Ebola, Obama.
The thing you seem to miss is that while this thing spins up our protection by isolation diminishes. Out of 8,000 we had ONE come in. How many will we have when the global burden is much higher? When it is a million will we get one hundred? Your calculations are static. The situation is dynamic.