Quoted from Bill Bryson:
For years, Britain operated a research facility called the Common Cold Unit, but it closed in 1989 without ever finding a cure. It did, however, conduct some interesting experiments. In one, a volunteer was fitted with a device that leaked a thin fluid at his nostrils at the same rate that a runny nose would.
The volunteer then socialized with other volunteers, as if at a cocktail party. Unknown to any of them, the fluid contained a dye visible only under ultraviolet light. When that was switched on after they had been mingling for a while, the participants were astounded to discover that the dye was everywhere—on the hands, head, and upper body of every participant and on glasses, doorknobs, sofa cushions, bowls of nuts, you name it.
The average adult touches his face sixteen times an hour, and each of those touches transferred the pretend pathogen from nose to snack bowl to innocent third party to doorknob to innocent fourth party and so on until pretty much everyone and everything bore a festive glow of imaginary snot. In a similar study at the University of Arizona, researchers infected the metal door handle to an office building and found it took only about four hours for the “virus” to spread through the entire building, infecting over half of employees and turning up on virtually every shared device like photocopiers and coffee machines.
In the real world, such infestations can stay active for up to three days. Surprisingly, the least effective way to spread germs (according to yet another study) is kissing. It proved almost wholly ineffective among volunteers at the University of Wisconsin who had been successfully infected with cold virus. Sneezes and coughs weren’t much better. .