Parts of Hungary and, in modern Belgium, the Brabant region, Hainaut, and Limbourg, as well as Santiago de Compostela, were unaffected for unknown reasons some historians have assumed that the presence of resistant blood groups in the local population helped them resist the disease, although these regions would be touched by the second plague outbreak in 1360–63 and later during the numerous resurgences of the plague). Other areas which escaped the plague were isolated mountainous regions (e.g. the Pyrenees). Larger cities were the worst off, as population densities and close living quarters made disease transmission easier. Cities were also strikingly filthy, infested with lice, fleas, and rats, and subject to diseases related to malnutrition and poor hygiene. According to journalist John Kelly, "[w]oefully inadequate sanitation made medieval urban Europe so disease-ridden, no city of any size could maintain its population without a constant influx of immigrants from the countryside".(p. 68) The influx of new citizens facilitated the movement of the plague between communities, and contributed to the longevity of the plague within larger communities.