Viruses are everywhere and not just the computer kind. Summer and winter we are surrounded by people coughing and sneezing, and we spend far too much time coughing and sneezing ourselves. If you live in the city, it's easy to see how these viruses get passed along, in crowded subways and elevators. But out here in the suburbs, where we have so much space and so little human contact, how on earth do the viruses get from one person to another? Do they develop legs like fleas, and jump? I think I have the answer, but you won't like it. It came to me in the supermarket, as I watched change being made by an unfortunate young woman who was all-too-obviously in the terminal stages of some highly infectious disease. She counted the money, counted it twice, and put it in my hand – an innocent Typhoid Mary at the checkout. Imagine this scene repeated millions of times every day all over the country. Medical researchers have spent more than a hundred years tracing the vectors of disease. Rats