Diseases like dysentery, cholera, typhoid etc., are more common in overcrowded human settlements. Why?

Role of overcrowded places in spread of diseases:

• Cholera, typhoid and dysentery are gastrointestinal diseases that spread due to poor sanitation. These diseases are carried by vectors like cockroaches which breed in unsanitary surroundings.
• Overcrowded places tend to be unsanitary. The disposal of human excreta is not done properly and drinking water can get contaminated by sewage.
• There is no periodic cleaning or disinfection of water and the contaminated water spreads the disease further in case of open excretion.