[BorisVSchmid]

Glanced at the abstract, and the amazon reviews. The medieval medical guilds were well aware of the clinical symptoms of the Black Death, so I wonder how Mike Baillie connects the characteristic buboes of the plague with meteor strikes?

I enjoyed reading this paper: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2632865/

The paper highlights several aspects of plague that were different between the second and third plague pandemic, and which caused a scientific movement that searched for alternative explanations for the Black Death - that is, until the Yersinia pestis bacterium got sequenced from multiple Black Death mass graves.

[nonbel]

I'm not familiar with the arguments in the book, but in general it could be both. The impacts could disrupt society (eg via crop failure) which leads to a breakdown of sanitary practices and poverty which leads to spread of disease.