In my book Obsession: A History, I argue that much of what we call Obsessive Compulsive Disorder is dependent on the social-cultural surround. Swine flu or H1N1 virus provides us with a real-time way of proving my point.
If you believe that washing your hands a lot, avoiding contact with other humans, wearing a mask, and the like are useful behaviors, at this moment you will be seen as a good citizen aiding in the stopping of the flu and protecting yourself and your family. If it turns out that the swine flu is an overblown media phenomena, then your behavior will suddenly revert to being compulsive and your thinking about the spread of disease will be seen as obsessional. You will be seen as the problem, especially by members of your family.
Everything depends on the context.
If we want to argue that OCD is a brain disease or a neurochemical disorder and we can spot with fMRIs or PET scans where in brain it lives or which neurotransmitters govern the OCD response, then how can the very same activity--protecting against contamination-- be pathological in one instance and normal in another in the very same brain?