Based on user testing with UARC:
Screen readers and other assistive technologies should be clearly notified after completing an action and/or when page content has changed or updated (e.g., after running a search). [WCAG 2.0 SC 4.1.2]]
Use either role=alert or aria-live=polite to indicate to users that the results set has been updated when they
- complete a search
- apply a filter to an existing results set
- sort the result set
Test with assistive technology - NVDA and VoiceOver to ensure this is working as expected.