During the 14th century, medicine was much less advanced than in modern times, and many important elements of epidemiology were not understood. For example, people did not generally understand how infections were acquired and spread.
Moreover, during this century, Europe in particular experienced many adversities. Famine was common, and the Black Death ravaged many regions in a short space of time. This had a large impact on urban life and medical practices.
Urban life was affected, as people who lived in cities were particularly affected by epidemics. Large populations were more likely to spread infections. Therefore, many cities lost a large percentage of their population, and with this, much of their economy and social life. Medical practitioners were also affected, as they were unable to cope with the tragedies or offer logical explanations. This pushed medical practitioners to turn to superstition and religious dogma, which in turn made advancements in medicine even more difficult to achieve.