Bacteria and viruses depend upon our biochemistry to survive which explains why some escape illness whilst others suffer.
Bacterial infections (like staphylococcus and streptococcus) proliferate within an acid environment, while viruses (like flus and the common cold) proliferate in an alkaline environment.
I've posted many long articles discussing how the changing seasons are responsible for over Alkalizing us and making us susceptable to the Flu virus but all most people seem to want in a list of what to eat and what to avoid.
ACID (Eat like this to get rid of flu) Avoid for a bacterial infection such as a sore throat.
cheese (may cause mucus build up)
ALKALINE (Eat these to help a sore throat) Avoid when you have the flu.
alcohol (remember this will lower the immune systems ability to function so won't help long term)
sugar (will also lower immune function)