We are a commune of inquiring, skeptical, politically centrist, capitalist, anglophile, traditionalist New England Yankee humans, humanoids, and animals with many interests beyond and above politics. Each of us has had a high-school education (or GED), but all had ADD so didn't pay attention very well, especially the dogs. Each one of us does "try my best to be just like I am," and none of us enjoys working for others, including for Maggie, from whom we receive neither a nickel nor a dime. Freedom from nags, cranks, government, do-gooders, control-freaks and idiots is all that we ask for.
In the 18th and 19th century Rome was a popular place for the idle rich to visit but not in the Summer when disease was prevalent. The disease was believed to be spread by "vapors". When I was a child in the 40's and 50's it was believed polio was spread by summer heat and humidity. My mother had polio as a child and was deathly afraid of it so she would pull the shades in the heat of the summer and we stayed in the house while our friends played. I was very thankful to Salk for inventing the polio vaccine. I can remember visiting an uncle once who was confined to a iron lung. It still gives me nightmares.
No, an epidemic is NOT defined by a single number, R. One needs to consider T, the incubation time between exposure and ability to transmit the disease.
An outbreak that took a year for an exposed person to infect one or more victims would be profoundly different from one where the disease only needed one day in the body before it was ready to infect another.
What's really cool is that you can model the rate at which infected mosquitos infect people with malaria with the same equations that predict whether a free neutron will cause a U-235 nucleus to undergo fission. The time cycles are just longer for the mosquito.
In the nuclear case, the "R" number in the article is called the propogation constant, which lets you know if you have a brick, a reactor, or a bomb on your hands.
another guy named dan
Add into this mix:
1. Epidemic diseases breaking into a virgin population (smallpox in the New World) are typically far more lethal than they are after long term exposure to a population as either the disease becomes less lethal as the infection becomes chronic (measles), or,
2. The number of survivors with temporary or long term immunity acts as a firebrake, or
3. Cultural practices evolve to add a barrier to infection, or,
4. Basic nursing can probably save a good percentage of victims, things like clean water, clean blankets, warmth, more likely to be found in a country where institutions aren't breaking down.