[crushthecurve]

We've been looking at digital contact tracing from the perspective of Australia, as we see a huge push for the COVIDSafe app, based on Singapore's TraceTogether app.

It seems the sensible order of questions is:

1) Do we have a contact tracing problem?

2) Does digital contact tracing generally solve it?

3) Is the specific app / implementation useful / safe / privacy-respecting?

It appears the national conversation almost entirely skips thinking about 1) and 2) and gets lost in the limited analysis of 3).

We had a deeper look at 2) in this recent piece:

https://blog.crushthecurve.today/why-should-you-install-the-...

[viraptor]

The post has a very city-specific view. (and it may have good points about that environment) Compare it to a regional town: minimal public transport, few/no dense residential buildings, no large offices. For me the app is literally a "does anyone I stood next to in the shop / petrol station test positive" indicator.

[crushthecurve]

In a regional context a bluetooth proximity app offers even less theoretical value.

A contact is only registered after 15 minutes of time spent within an estimated proximity of 1.5 metres (itself a primitive model of infectious disease transmission based on a 1942 paper). Note other countries set the distance at 2 metres.

As outlined in other comments in this thread, close contact rules include anyone in a room for more than 2 hours, so even though all close contacts have to be manually interviewed (there is no instantaneous notification and isolation) for most social situations close contacts won't be registered through crude estimates of proximity: home, family / friends, work all require thinking about and providing contacts.

When you strip out all the situations that aren't beneficial, that starts to leave public transport in major metro situations where commutes are greater than 15 minutes.

Keep in mind that also implies the end of any social distancing (as otherwise no contacts are registered). That seems obvious, as public transport becomes overwhelmed if capacity is significantly reduced.