Because of cleanliness jewish people were less likely to catch it.Many people of the time therefore blamed the joooos!!!
The Jews basically handled the black death like Leviticus says to handle leprosy. One of the Italian kingdoms decided to do the same, making a rule that if someone gets sick with it they should be set aside for 40 days from everybody else. The way they said "40 days" in that old Italian dialect is where get our word "quarantine" today.