SAN FRANCISCO (Reuters) – Cerner Corp and Athenahealth Inc, two leading U.S. electronic health record providers, said on Thursday they are working with Apple Inc to develop applications that leverage Apples mobile health service HealthKit. Cerner and Athenahealth representatives said they are building integrations with HealthKit and working with Apple. Previously, Apple announced a partnership with rival electronic health record company Epic Systems. Apple did not respond to a request for comment. …