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Comment by jonathanstrange | Hacker News Reader

I've been wondering for a while why countries do not test people randomly like in phone surveys, i.e.randomly pick several thousand persons from a region and test them. Like in phone surveys you need to compensate for biases created from people declining to be tested, of course. It would be expensive, but it seems to me that it would yield a good picture of what is going on.

Maybe I'm missing something obvious and this is not possible, though.

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Wuhan's capabilities up until about two weeks ago were a max of two thousand tests a day. Even now, they are only able to test more patients because of horizontal scaling, aka building more machines to eliminate bottlenecks in the RT-PCR pipeline. The rest of the world is significantly behind. The test may also be run several times per person because there is evidence that there is a high false negative rate while patients are still asymptomatic.

There are so many people suspected of infection in just about every nation that there is simply not enough tests to go around to test people at random.

Switzerland has the capability to run 1'000 tests per day right now, they currently are not at the limit for testing.

I am not aware of countries that test completely randomly. But many countries have so-called sentinel surveillance, where 1-5% of family doctors (general practitioners) send in samples to a lab from patients who appear with influenza-like or respiratory symptoms. This is how they monitor the spread of different kinds of influenza strain. In principle, if there’s enough testing capacity and it’s judged worthwhile, this could be expanded to also test these samples for SARS-CoV-2.

https://www.ecdc.europa.eu/en/seasonal-influenza/surveillanc...

This makes it sound like at least one German state has tested for coronavirus as part of their sentinel surveillance, but I’m not sure if that test was completely random:

https://twitter.com/MSI_BW/status/1233333090896039936

The UK is doing this now: https://www.reuters.com/article/us-china-health-britain/uk-c...

Not quite random since they are only testing people with cold and flu symptoms but these are spread around the country in order to act as an early warning system for spread of the virus.

It might have to do with the testing technology. If your false positive rate is high, but you’re only testing people with clear symptoms, it’s fine. But if you test random people the data could be too noisy

They are in the UK, well not completely at random but a number of health centres and hospitals are now testing everybody who has flu-like symptoms.

I'm still not clear what "testing" entails. I'm not going anywhere near a hospital to be packed with hundreds of other potential cases if I can avoid it.

On the other hand, if we had a spit-and-mail test, this could turn into the biggest DNA harvest operation of all time.

In the UK it is now being done on a "drive through" basis at some hospitals. You park and nurses in protective gear come out to take a saliva sample while you stay in the car. Then you drive home, self isolate and wait for the results.

The area affected by the virus in Italy contains 20-30m people. If there are 10000 infected, they are only 0.05% of the population. A country would need to test tens of thousands of people to get any meaningful results.

In Switzerland they currently have a good picture of whats going on. They were able to trace backe where all infected people got the disease from.

Yes in Switzerland and all the new cases originated in different place of Italy. So it seems that in Switzerland when people are back from Italy and having symptoms, they look for help and are tested. But as it is very unlikely that all these people were in contact with the 650 people detected in Italy (most of them were back from Milan, Verona, and not from the lockdown cities, my fear is that Italy is facing a different order of magnitude of cases. And that's why I was interested in potential model to simulate this.

Not sure about Italy, but Imperial college in London did estimates in January for how many in Wuhan were infected based on internationally infected people and the catchment area of Wuhan airport. https://www.imperial.ac.uk/news/194815/coronavirus-outbreak-...

yes I just heard from the team that did the sequencing of the virus in Italy they now believe that the virus has been circulating there for weeks without being detected...

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