10 C.F.R. § 603.655
If an expenditure-based TIA provides for periodic audits of a for-profit participant by an IPA, the contracting officer must specify the frequency for those audits. The contracting officer should consider having an audit performed during the first year of the award, when the participant has its IPA do its next financial statement audit, unless the participant already had a systems audit due to other Federal awards within the past two years. The frequency thereafter may vary depending upon the dollars the participant is expending annually under the award, but it is not unreasonable to require an updated audit every two to three years to verify that the participant's systems continue to be reliable (the audit then would cover the two or three-year period between audits).
10 C.F.R. § 603.655