Totally amazing that doctors don't know what causes the flu. Gabriel Cousens may be the only md that does. For one thing, the flu is not contagious. The trigger is, yes, but the flu itsself is not. I never get the flu, or a cold, even if I'm in a roomful of people that do. The deal is to be clean inside, primarily not having any mucus. Colds and the flu are cleansing mechanisms to rid our body of mucus. If you have a whole lot of mucus then you may even get a fever, which melts mucus so it can come out our pores. Colds and the flu, as well as hay fever, are directly related to poor diet. Read Cousens, David Wolfe and Arnold Sheet.