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Comment by okintheory | Hacker News Reader

Immediate reaction: I'm sorry they settled on blue-tooth induced proximity. It seems likely to be a poor approximation of "epidemiologically relevant proximity". I would like to see research supporting the efficacy of this approach. I suspect they would conclude they need a geolocation-based approach. This will make privacy even more difficult.

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If you're in "epidemiologically relevant proximity" you're almost surely also in bluetooth proximity. Quarantining a few more people than necessary is not a big deal and totally worth the privacy tradeoff imho.

I wonder if there would be a way to do something like this but using WiFi access points that are available. The phone could track access points as they come into range (don’t need to connect) and time stamps and cross correlate with others. Seems a bit less intrusive and wouldn’t require Bluetooth but obviously there wouldn’t be as much coverage.

sharing a timeline of access points and timestamps is somewhat similar to a timeline of gps coordinates and timestamps. there is a lot to infer from such data and can potentially reveal the identity of the person who got sick and shared their data

Is that true? I'm more worried about false negatives on connections. Two concerns (as a layperson):

1) Transmission via surfaces is thought to be important (afaik). You don't have to be in the same place at the same time to transmit.

2) My bluetooth seems pretty slow and unreliable when connecting to my headphones. Is it reliable for logging ~50 proximities during my trip to the supermarket?

Ad. 2 - it is not that bad: duration of proximity is correlated with both infection probability and connection probability.

1) That would be difficult to solve. If we used position reporting, and considered an area infected for a few days after an infected person arrived, it would most likely lead to unmanageable amounts of false positives.

2) Scanning is mostly just listening and waiting for other devices to send beacons. With one discoverable device nearby, it might take a moment to hear anything. With 50 devices nearby, you scan should be spammed with results.

You might have missed a few devices if you were unlucky and moved out of range before they got a successful beacon through. However, in that case you could use second-hand proximity to find the "lost" contact through some of the successful ones.

> 1) Transmission via surfaces is thought to be important (afaik).

According to Hendrik Streeck, a leading researcher in Germany, this may not be the case: https://youtu.be/VP7La2bkOMo?t=231

They are working on a more formal study of this but indications are that the viruses that other teams have found on surfaces may be "dead" (in the sense that they cannot actually replicate anymore and therefore are not bioactive relatively soon after leaving host organisms).

Video only in German, sorry, sure this will get publicized internationally if the study confirms the indications.

as you say it _may_ not be the case. So, as long as no one knows for sure...

This totally contradicts another study [1]. They found that the virus is "viable and infectious in aerosols for hours and on surfaces up to days (depending on the inoculum shed)."

[1] https://www.nejm.org/doi/10.1056/NEJMc2004973

that's only a letter not a paper.

and they only measured the quantity, not whether the viruses they found after x hours could actually still replicate.

Thank you for the hint (in the reference [1], the measurement done as in [2], which states "Collected aerosols were analysed by quantitative real-time polymerase chain reaction (qRT-PCR) and by virus titration"), although I then don't get why the paper [1] writes that the viruses are "infectious".

[1] https://www.nejm.org/doi/10.1056/NEJMc2004973 [2] https://www.eurosurveillance.org/content/10.2807/1560-7917.E...

They should do a dead-simple PoC to demonstrate this actually working with Bluetooth. Just make a stupidly simple test app, get 100 volunteers to install the app, have them all wear masks etc. while walking around randomly in the same big room for half an hour.

Then see what the false negative rate is - unless the average number of "others seen" is close to 100, this isn't going to work.

I saw a video clip of a test like that, though it didn't contain any results. What makes you think that the developers didn't test it?

Because it's an obvious sticking point, everyone's had trouble with bluetooth not recognizing the same ol' headset, the burden of evidence is on the developers. And if they have done the test and not published the results, I'm twice as skeptical.

Surfaces can be cleaned easily and should be cleaned frequently. (Eg on public transport.)

Furthermore any kind of app will only reach a subset of the population. (Senior citizens are unlikely to install this app.)

Yes, bluetooth drivers are a horrible hellscape of cyberspace, but it's probably because connecting to a sink/source (speaker/mic/camera/whatever) sets up the corresponding audio/media/etc channels too, and the interaction of the relevant components (pairing, PIN, kernel modules, gstreamer or who knows what) is what requires a very fragile dance. I have no idea how broken the BLE part is.

Firechat doesn't seem that bad and it uses Bluetooth too.

The proximity tracing does not have to be perfect, just like social distancing or face masks do not have to be perfect. They just need to be effective enough to reduce R < 1.

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