“Interestingly, it’s possible that practices related to the observance of Passover helped to protect Jewish neighborhoods from the plague. Passover is a week-long holiday commemorating Jews’ escape from slavery in Egypt. As part of its observance, Jews do not eat leavened bread and remove all traces of it from their homes. In many parts of the world, especially Europe, wheat, grain, and even legumes are also forbidden during Passover. Dr. Martin J. Blaser, a professor of internal medicine at New York University Medical Center, thinks this “spring cleaning” of grain stores may have helped to protect Jews from the plague, by decreasing their exposure to rats hunting for food—rats that carried the plague.”