Bacterial Infection

I am finding, in our offices and in daily conversation, more and more that people don't have a firm grasp on what illness and disease really are. This is not any one persons fault. The public's understanding is subject to what they are told by the 'authorities' of any field. So what are the 'authorities' on health defining disease as? I hear plenty of different points of view on this question. Lets narrow things down to one type of disease for now.