how would a person develop those diseases that dont spread by contact with asick person ?

That would depend on the type of disease. For example :

• Deficiency diseases like scurvy, Kwashiorkor, anaemia etc are caused by inadequate diet.
• Inherited diseases like haemophilia are caused by passing of defective genes from parents to offspring
• Degenerative diseases like arthritis are caused by wearing away of organs and tissues usually with age
• Mental diseases like depression and paranoia are caused by brain damage
• Hormonal imbalances cause disorders like hyperthyroidism, diabetes etc.
• Malfunctioning of the immune system causes problems like allergy