Let's start with this photo. It's a photo of some statistics compiled by PLM using patient data entry for the benefit of other patients.

You can see that patient communication is indirectly happening when one patient fills out their "charts" and another patient can benefit from the data. This is all made possible by the quick and easy Internet sharing and middlemen that staff the website. It acts a lot like a recommender system, but it's not as forceful as it might be on another website where you're forced to "receive" this communication - it's more about your needs, legitimately.