There is substantial scientific evidence supporting the occurrence of human-to-human transmission of the virus.

One question, of course, is what the scientific evidence suggests about human to human spread of this virus. And that's already where it gets complicated, so let's do it bit by bit:

So that’s part of the scientific question answered to my satisfaction at least: There’s pretty good evidence of some human to human spread of this virus. Now the question is: Okay, but how likely is that to happen and under what circumstances? And that’s where it gets even less certain.