This is indeed a clever advertising initiative designed by Publicis, India. It banks on a simple and clever idea, suitable for the limited number of target audience.

This initiative was for IFFECO-Tokia was designed during summer 2009 when the swine flu alert was in full swing. The company wanted to make awareness among its employees about the necessity of washing their hands frequently to prevent swine flue. They communicated this message in an interesting way.
A poster was placed before washroom doors. The copy was- This is how … spreads.
Every time someone visits the washroom they will naturally push their hands against the poster and it will eventually get dirty. Then the copy becomes clear- This is how swine flu spreads.
CREDITS
Advertising Agency: Publicis, Gurgaon, India
Executive Creative Director: Emmanuel Upputuru
Creative Group Head / Copywriter: Sudhir Das
Creative Director: Anindya Banerjee
Associate CD / Art Director: Sunny Johnny