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You may be misunderstanding the purpose of contact tracing? It's not to guess whether a patient you have is infected. It is to find the people that patient has
by feral 6y ago
You may be misunderstanding the purpose of contact tracing?
It's not to guess whether a patient you have is infected. It is to find the people that patient has infected before those infect more people.
If things are being run properly:
1. Someone shows up with the disease. (Tests positive, or clinical.)
2. You find their contacts, either by app or interview or both.
3. You tell those contacts to quarantine, hopefully before they've become infectious, breaking onward spread.
4. If they test negative and don't display symptoms, they stop quarantine.
Unless you mean to test everyone every day? Sounds good, but then you need way more tests than countries have been able to make so far, and they have to be very sensitive and specific too, even before someone is infectious.
- yummybear 6y agoRegarding 3) - should they quarantine regardless or just if the get ill?
- enitihas 6y agoThey should quarantine regardless, since asymptomatic people are also spreaders. Ill people sre anyways getting quarantined even without any tracing.
- chosenbreed37 6y ago> Regarding 3) - should they quarantine regardless or just if the get ill? I guess they have to quarantine. Not only them but anybody else that came into contact with and so and so forth :-)
- feral 6y agoProbably. I would say that depends on the overall strategy. If pre-symptomatic people infecting others is a big issue, then it's probably worth the cost of quarantining folks who display no symptoms until you are sure they aren't sick. Obviously that means you quarantine a lot of people who don't later get sick. That sounds draconian, but its a lot better than lockdowns.
- fragmede 6y agoIt it depends on the pandemic. The reason COVID-19 has upended the world is that our usual metric "if they get ill" doesn't work. It doesn't work in this case, because many people with the virus show no signs while they are contagious, with some (many?) never showing signs they were ever sick. Worse, because COVID-19 is new, we are still learning details about it performs. The current recommendation to quarantine for 14-days is based on what little we do know - which is that people exposed to the virus may show no symptoms for 14-days. There are cases of it taking more time, and there are also cases of it taking shorter time, but 14-days is what's currently recommended. Because we're still learning how the virus performs, testing is far from foolproof. A test that says negative for the virus just means that the test says negative. The swap could have missed the virus even though a person has it. Thus, if reopening is to avoid a second wave of cases, they must quarantine until either the 14-days are up (and even then), or we (humanity) learn enough more and are able to give tests that are more widely trusted. "Quarantine regardless" is pejorative - it makes it sound like quarantine is just for the sake of it. With more knowledge and better technology, the 14-days could possibly be reduced, but the quarantine is one of the oldest medical technologies we have - an empirical test for "do you have the virus".
- moultano 6y agoYes, they should quarantine until they're able to get a test and test negative. We have a lot of evidence of asymptomatic and presymptomatic spread.
- arrrg 6y agoYou are infectious about 1-2 days before the onset of symptoms. Actually, at the onset of symptoms many are already getting less infectious. That’s why this one’s hard to catch up with. You need to be very quick when contact tracing. So, yeah, absolutely, you should quarantine after contact with a known infected person, no matter whether you have symptoms or not.
- joshuamorton 6y agoThey should quarantine until tested. The idea is that with mild social distancing + contact tracing + good testing infra, you can track virus spread faster than the virus actually spreads, keeping outbreaks localized.
- joshfraser 6y agoRegarding #3 you give them a quick, free test to determine whether they should quarantine or not.
- colmvp 6y agoIn an ideal scenario, agreed, but very few countries have enough tests to test non-essentials workers or people who are experiencing minor symptoms.
- dhosek 6y agoWith one notable exception, most countries are at least working on this if not having reached this level already. Just because the country with the largest number of infections is screwing up the testing doesn't mean every country is.
- DennisP 6y agoSchneier seems to misunderstand this as well. Contact tracing is to find the next people to test, because you can't test everyone every week. Schneier calls it a "false positive" when transmission doesn't occur, but as far as contact tracing goes, it's only a false positive if no transmission could have possibly occurred.
- abrichr 6y agoInteresting, thanks for the explanation! Do you know where can I learn more about contact tracing?
- s1artibartfast 6y agoThe authors point, as I understand it, is that the app is not a useful tool for contact tracing due to the propensity for false responses. The R0 of of the virus is somewhere between 2 and 5, meaning that the average person passes it on to 2-5 people. How many people does urbanite come within proximity of within a 14 day period, 100? 1000? Also, some portion of those 2-5 may never have come in contact due to surface transmission, or be obvious without the app, such as intimidate family. The question then becomes who will trust the app enough to self quarantine for 14 days.