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
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.
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