The nature of the HealthUnlocked site is that members can join any number of communities and although I will from time to time remind people about guarding their privacy, and what people can and can't see, it is at the end of the day down to an individual what they choose to share, and where.
When you post, you tick a box to post "only followers in my community" or to "everyone" - if you do not wish people from other communities to read what you post here (or vice versa) please ensure you tick the correct box - it defaults to "everyone". Please also note that if that box isn't ticked, a Google search might also show your post.
If you still want to contribute to different groups but keep them separate, I would suggest that you create different profiles with different email addresses (eg set up new Gmail accounts, it's very easy and free).
If you have any questions or queries, please don't hesitate to message me.