For the sources of the epidemic illness, I performed a little investigation:

1. The serious flu in 1918 caused 21 million people's death, that was happened in Spain first then spread all over the world. Some people said the soldiers from east brought the virus back but that seems like rumours. Scientists believe that the virus were from swine. Anyway Spain was the first place where this flu took place.

2. The worldwide keratitis epidemic is not from China, too.

3. It is well know that syphilis and opium originated from the west world and then transferred to China.

4. The first AIDS virus case was found in US, although people insist that the viruses were from Africa.

So I don't think China is the source of all epidemic diseases.