Which statement best describes an epidemiologic transition? 

A)  It happens before a demographic transition. 
B)  It happens when mortality is due mainly to childhood infectious diseases rather than adulthood chronic diseases. 
C)  It happens when mortality is due mainly to adulthood chronic diseases rather than childhood infectious diseases. 
D)  It is the same as a demographic transition.

An epidemiologic transition is a shift in the pattern of mortality from infectious diseases to chronic diseases as countries develop economically and socially. Option C correctly describes this transition as occurring when mortality is due mainly to adulthood chronic diseases rather than childhood infectious diseases. Option A is incorrect because the demographic transition refers to changes in birth and death rates as a country develops. Option B is incorrect because it describes the pattern of mortality that existed prior to the epidemiologic transition. Option D is incorrect because while the epidemiologic transition is related to demographic changes, it is not the same thing.