My understanding is that the way the contact tracing app would work (at least, the Apple/Google one, not sure if the gov't has settled on that one yet) is that the notification goes directly to the user, and the link is not actually exposed to public health authorities. So, for example:
- You see an SP. Your phones, by virtue of being close to each other, record a "proximity event".
- Within 14 days of the encounter, the SP tests positive for covid-19. (Not necessarily contracted from you.)
- Public health authority asks SP if she has the app. If she does, they activate a feature on it to broadcast a notification to all contacts in the past 14 days of possible exposure.
- You receive the notification, giving you the opportunity to get tested / isolate yourself.
- However, the fact that the contact occurred between you and the SP, is never disclosed to the public health authority.
This seems like the best of both worlds, in that contacts get promptly notified, but there is no exposure for the industry / individuals partaking.
There are other downsides to proximity-based apps, though. For example, Bluetooth signals travel pretty readily through interior walls, so the app can't reliably tell the difference between an actual encounter in a room, and you happening to come within a few metres of a person in an adjacent condo unit or upstairs/downstairs from you. So there's bound to be a lot of false positives, possibly leading to misplaced panic and eventually people becoming desensitized to notifications, not bothering to follow up and get tested etc.