Did fewer Jews die of the Black Plague because of ritual washing?

Question

I've frequently heard the claim that fewer Jews died of the Bubonic Plague than their Christian neighbors in the Middle Ages because Jews took regular ritual baths (mikva) and ritually washed hands before eating (netilat yadaim), while the Christians rarely washed themselves. Supposedly this lead to antisemitism and harsh persecution because the Christians saw their Jewish neighbors surviving and assumed they had control of the plague and were deliberately cursing them. Is there any truth to this claim?

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I found some sources making this claim from citations in the Wikipedia Article "Black Death Jewish persecutions":

Example from jewishhistory.org: "And even if Jews died at a lesser rate, it can be attributed to the sanitary practices Jewish law. For instance, Jewish law compels one to wash his or her hands many times throughout the day. In the general medieval world a person could go half his or her life without ever washing his hands."

Anna Foa, The Jews of Europe After the Black Death (2000), Page 146: "There were several reasons for this, including, it has been suggested, the observance of laws of hygiene tied to ritual practices and a lower incidence of alcoholism and venereal disease"

Answer 1

So, the JewishHistory.org website touts the hygiene of the ghettos in this way:

The sanitary conditions in the Jewish neighborhood, primitive as it may be by today’s standards, was [sic] always far superior to the general sanitary conditions.

However, when I started digging into the citations given by Anna Foa for her claim, I soon bumped into this:

The exceptionally miserable and unhygienic external environment in which the Jewish settlements live must be added as a constant pejorative of all their morbid manifestations. (1)

This author, an Italian scholar named Livi, claimed that the Jewish ghettos were so dirty that they actually weeded out weak immune systems, which led to lower death rates. We might guess this scholar was an anti-Semite. So, is there evidence refuting this? Anna Foa cites an English-language article (2) but it contains no claims about hygiene at all. In fact she has made a mistake, because her bibliography also points to longer Italian-language version of the same article (3), which contains this footnote disagreeing with Livi:

Nor should it be forgotten that, if the environment in which Jews lived in the era of the ghettos was particularly unhealthy, the trades they exercised were among those with lower risks of morbidity and professional mortality, and that their living arrangements, pursuant to religious requirements, were particularly favorable for increased resistance against causes of lethality. (3)

No source is given for the author's claim.

The other source given by Foa is correctly cited. In translation, it states the following:

What we know about the evolution of mortality, indicates that throughout it appears significantly lower than that of the Christian populations. The causes of this more favorable situation — very well documented from the end of the eighteenth century — are certainly many, ranging from compliance with hygiene standards prescribed by religion, rooted in moderate customs for eating and drinking, the low incidence of venereal diseases, and an economic level on average higher than average. (4)

The citation for this paragraph, however, is Livi! So back I go to Livi, vol. 2, looking for proof of this assertion; but all I can find there is an overload of data, accompanied by the bare observation that the "Jewish race" stands apart in mortality statistics. Evidently what is "well documented" is the low death rate, not the reasons for it.

Not only is there no proof of causation for this claim, there is no responsible scholar pushing the claim all the way back to the Black Death. Anna Foa is not making such a claim herself, as she is talking about the period 1527–1592 (the Black Death lasted from 1346–1353).

I think there is good reason to find this claim historically dubious. It appears to be a mischaracterization of Foa's book, which itself cites some bare assertions which need to be more closely examined.

_{(1) "L’ambiente esteriore eccezionalmente miserabile e poco igienico nel quale vivono le colonie israelitiche devesi considerare come un costante peggiorativo di tutte le loro manifestazioni morbose." Livio Livi, Gli Ebrei alla luce della statistica (1919), vol. 1, p. 199
(2): Roberto Bachi, “The Demographic Development of Italian Jewry from the Seventeenth Century.” Jewish Journal of Sociology 4/2 (1962): 172–91
(3) "Non si deve dimenticare inoltre che, se l’ambiente in cui vivevano gli ebrei nell’epoca dei ghetti era particolarmente insalubre, i mestieri da essi esercitati erano tra quelli che comportano minori rischi di morbosità e mortalità professionale, e che il regime di vita conforme alle prescrizioni religiose era particolarmente favorevole per una maggiore resistenza contro le cause letali." Roberto Bachi, "La demografia dell'Ebraismo italiano prima della emancipazione." La Rassegna Mensile di Israel (1939): seconda serie, Vol. 12, No. 7/9, p. 310
(4) "Ciò che conosce sull’evoluzione della mortalità, indica che ovunque essa appare sensibilmente inferiore a quella delle popolazioni cristiane. Le cause di questa più favorevole situazione — assai ben documentata fin dall’ultima del XVIII secolo — sono certamente molte, e vanno dall’osservanza di norme igieniche prescritte dalla religione, a radicati costumi di moderazione nell’alimentazione e nel bere, alla bassa incidenza delle malattie veneree, ad un livello economico mediamente più elevato della media" Livi Bacci, M. (1983) 'Ebrei, aristocratici e cittadini: precursori del declino della fecondità', Quaderni Storici XVIII (54), p. 924}

Answer 2

Compliance with rules for hygiene could not reduce mortality from plague so much -

...today it is accepted that the percentage of Jews who died in the plague was not less than the percentage of non-Jews (relative to the size of the community).

Barbara Tuchman, A Far View: The 14th Century, The Hall of Devils, Dvir Publishing, Tel Aviv, 1995.

But -

it is true that Poland did survive the Black Death relatively unscathed. In addition to Poland's relatively sparse population, a key factor is that King Casimir the Great wisely quarantined the Polish borders. By holding the plague off at the borders, the disease's impact on Poland was softened.

Gottfried, Robert S. Black Death. New York: The Free Press, 1983.

During Kazimierz's reign, the Black Death, a pandemic infection, swept across Europe, killing millions. But Poland established quarantines at its borders, and the plague skirted Poland almost entirely.

Zuchora-Walske, Christine, Poland, North Mankato: ABDO Publishing, 2013.