Yeah, there's something about that part of the world that's advantageous to microbial diversity. Lots of heat and humidity and decaying organic matter, and it's been populated by humans for so long the bugs have had more time to adapt to using us as hosts. You see similar things coming out of places like the Congo and Amazon jungles, but the same history of civilization China prides itself on also elevated our exposure levels earlier, and to a higher degree, than the rest of the world. Wherever you find concentrated humans you find concentrated filth. It's always been a part of life, but it wasn't until we started densely packing ourselves into cities that plagues really started racking up the death toll. It's just nature's way of thinning overpopulated herds.