When did american suburbs increase dramatically, at a rate of 40 times that of cities? (between the years 1950s, 60s, 70s, or 80s)

That is because the US economy was the best in the world. They were manufacturing on an unprecedented level so they needed a lot of factories and a lot of workers. The suburbs started developing because the workforce that was larger than ever needed somewhere to live, so people started moving to the suburbs and they were built rapidly.

The constant presence of diseases or infectious agents within a given geographic area or population group. it may also refer to the usual prevalence of a given disease with such area or group. it includes holoendemic and hyperendemic diseases. a holoendemic disease is one for which a high prevalent level of infection begins early in life and affects most of the child population, leading to a state of equilibrium such that the adult population shows evidence of the disease much less commonly than do children (malaria in many communities is a holoendemic disease). a hyperendemic disease is one that is constantly present at a high incidence and/or prevalence rate and affects all groups equally. so probably family history.