A violent pestilence which ravaged Europe between March, 1348, and the spring of 1351, and is said to have carried off nearly half the population. It was brought by sailors to Genoa from south Russia, whither it had come from central Asia. During March and April, 1348, it spread through Italy, Spain, and southern France; and by May of that year it had reached southwest England. Though the Jews appear to have suffered quite as much as their Christian neighbors (Höniger, "Der Schwarze Tod in Deutschland," 1882; Häser, "Lehrbuch der Gesch. der Medizin," iii. 156), a myth arose, especially in Germany, that the spread of the disease was due to a plot of the Jews to destroy Christians by poisoning the wells from which they obtained water for drinking purposes. This absurd theory had been started in 1319 in Franconia (Pertz, "Monumenta Germaniæ," xii. 416). On that occasion punishment had fallen upon the lepers, by whose means the Jews, it was alleged, had poisoned the wells. Two years later, in the Dauphiné, the same charge had been brought against the Jews. In 1348, once the accusation was raised, it was spread with amazing rapidity from town to town.
Although the Jew-baiting was scurrilous, irrational, and hateful, it's revealing in another respect. How many times have you read atheists say Christians traditionally attribute natural events to God's direct action? How often have your read atheists say Christians traditionally attribute plagues to divine judgment?
Yet these medieval Christians did not attribute the plague to divine judgment or direct divine action. Rather, they suspected the plague had a natural cause.
Moreover, although they were mistaken about the transmission of this particular pathogen, there's nothing irrational about considering the public drinking water supply as a possible source of contagion. Some epidemics have a common point of origin. Indeed, infected drinking water is a source of cholera. It can be reasonable to trace some epidemics back to common source.
So the notion, popularized by atheists, that prescientific Jews and Christians (as well as pagans) automatically ascribed natural events to direct divine action, or divine judgment, in the case of epidemics, is a simplistic and ignorant urban legend.