Symptoms
After you create a topic feed in Microsoft Skype for Business 2015 (Lync 2013), you find that there's no option to only apply it to a subset of rooms. Additionally, you cannot filter the top-level search to a specific chat room.
Resolution
To fix this issue, install the January 3, 2017, update (KB3141468) for Skype for Business. Note Lync 2013 was upgraded to Skype for Business in April 2015.