In an experiment conducted by psychologists Nemeroff and Rozin, people were asked how they would feel about wearing a particular jumper that had never been worn and in addition been recently laundered.
"Not surprisingly, people said they had no problem wearing the sweater. The experimenters then asked them to imagine that the sweater had been worn by someone who had contracted AIDS through a blood transfusion [but] been laundered a few days ago, and that the person with AIDS had worn it for only thirty minutes, but suddenly people didn't really want to wear the sweater. Even though they knew there was no health or hygiene issue, the superstitious theory of contagion kicked in and they could not bring themselves to wear it. Rozin and his colleagues varied the imaginary sweater owners, and discovered that the idea of the sweater having once belonged to someone who personified evil, such as a mass murderer or a fanatical leader, elicited the strongest reaction from people. In fact, Rozin's results revealed that people would rather wear a sweater that had been dropped in dog faeces and not washed (raising genuine health concerns) than a laundered sweater that had once belonged to a mass murderer."
Richard Wiseman, Quirkology: The Curious Science of Everyday Lives, Pan Books, London 2008, p. 105, 106
for more detail on contagious thought, see