True but it takes enough of them coming back sick to infect just one innocent person not associated with anything other than being in the wrong place at the wrong time.
Quite true. However, it appears that some large number, probably something around 100 or more, had contact with the Duncan, the nurses and others in the early stages of their disease, and thus were potentially exposed.
Of those, none, yet, appear to have caught the disease. This indicates very strongly that it just isn’t very contagious at that stage, as the docs have been saying. Which is a very good thing indeed.