" when we think about health, we think about societies and communities. on the other hand when we think about a disease we think about individual sufferers" - why?

There is no as such categorization that when we think about health, we think about societies and communities. On the other hand when we think about a disease we think about individual sufferers because an epidemic disease also spreads in the society and not restricted to the single individual. 

However, disease affects the normal body functioning of the person. While health can include both personal health and community health. Personal health is the state of physical, mental and social well-being of an individual. It includes bathing regularly, brushing teeth, washing hands before eating, etc. Community health is the maintenance, protection  and improvement of the over-all health and well-being of the community. Community health includes proper sanitation, clean drinking water, proper waste disposal, healthcare services, vaccination, medical aid, etc.