They were perpetuated by filth that harbored rats, and contaminated water supply. It was not uncommon for Europeans to throw their garbage and even human wastes out of the window. They figured that stray dogs would eat whatever they threw out. It is hard to be specific. Until recently trash quantity was calculated by volume not weight.
Volume is dependant upon how much the trash is compacted.
Weight is influenced by moisture content, which varies greatly depending upon climate and weather conditions. The various studies that have been conducted vary too greatly to get a clear picture of per capita refuse per day. Studies fail to substantiate the notion that Americans are more wasteful than similar civilizations of the past. Note that the nature of the waste varies greatly from one civilization to another. There is an archeological account of Native Americans in Colorado about 6500 BC who killed 200 buffalo in one day and butchered 150 of them, carrying away enough meat to feed 150 people for 23 days.