The only information users can share with the app is a positive diagnosis. Sharing your positive diagnosis with the app is completely voluntary. If you do decide to share it, the information will never leave your phone. The only information that will leave your phone is the log of randomly generated keys that your smartphone has been emitting via Bluetooth as part of the Exposure Notification system for the last 14 days. These keys do not encode any personally identifying information or location data, and have no meaning outside of the phones with which you have come into close range of while both phones had Bluetooth enabled and Exposure Notifications turned on.
The app also collects anonymous usage statistics. These statistics do not contain any personally identifying information or location data either, and will never be shared outside of the app without your explicit permission. Learn more about Share App Use Statistics here.