The Church was hugely powerful: Belief in heaven / hell, No education, so people learned from church, God punishes sinners, Disease is a punishment sent by God
Galen (Roman physician) developed the idea with theory of Opposites. For example, if you had a phlegmy cold, this should be balanced by eating something hot eg pepper
Local governments tried to control by building new cemeteries, close Parliament in 1349, enforcing street cleaning in cities, but this often didn't happen