Official Google Blog: A remedy for your health-related questions: health info in the Knowledge Graph
Search Engine Land says this initially covers more than 400 issues and admittedly "speculates" this is to help improve rankings of other sites (LOL. What a hoot as Google takes over yet another category with its own content).
Google Introduces Rich Medical Content Into Knowledge Graph
Bottom line: If you are in the health niche, especially medical issues, if it wasn't hard enough to compete with WebMD you either need to reconsider your strategy or be prepared to be blown out as Google takes over this massive amount of searches with its own content.
For your business strategies you need to pay attention to what is happening. This may open up some opportunities, but for those relying on Adsense clicks, for example, on general health article sites, expect an income drop. For other niches next on Google's radar you need to evaluate if what you are doing makes long-term sense.