auto refresh segment with contacts

Hi

We are creating a segment of users who have placed an order in last 1 week and sending them a customer satisfaction survey.

The segment is used in a campaign to trigger the emails.

The problem i am seeing is that the segment always shows stale contact count until someone manually goes and refreshes them.

We want that any any contact created should automatically be included in the segment and the campaign.

How can we achieve this automation step?

Thanks