Epidemic Spread - Who / How

This is obviously a very big and important question. In my previous post I mentioned how in an area (e.g., earth) where everyone is susceptible to a new "nasty," and it is being spread from human to human, that isolation and containment procedures are one way to slow down that transmission process and, hopefully, slow down the process.

So many questions with this. But two very practical questions are: by whom is it being spread (e.g., at what stage of infection) and what is the actual mechanism of transmission. If it is spread human to human, then who is more responsible for the spreading - which age group is more susceptible, e.g., children or adults.

With respect to the first question, I came across an interesting site (google search = pandemic isolation) where there is some evidence that it's a little of both but in significantly different ways. It turns out that school age children may spread it to more people in a geographic area (neighborhoods) but adults are more responsible for spreading it to potentially vastly larger numbers through going to work and thus exposing others at work to it, and those workers then go back into their various neighborhoods.

The even bigger issue was with the spreading that comes from transportation arrangements. It's one thing if you travel within the state for business, it's totally another thing if you fly, for example, on a business trip from San Francisco, to Toronto, To Boston, To Atlanta. It's easy to get that picture.

I remember a year or so ago when the SARS issue was prominent and how I was aware of a few people in my office building who had traveled to Hong Kong, Taiwan, China on a recent business trip. I didn't do anything different then, well maybe I didn't use the exit on their side of the building as often, but it got me thinking.

n.b. edited 5/31/08 for grammar and clarity.