Are you sure that Germany does not perform extensive testing? I admit that reddit comments should not be used as sources but I would love to know more about German approach to testing.

https://www.reddit.com/r/askscience/comments/fguheu/why_have...

Earl_of_Northesk: The RKI is conducting random sample testing to keep track of Influenza in Germany. These tests now also test on COVID-19. So far, not a single prior undetected case of COVID-19 has shown up in these samples. It is thus highly likely that the extensive early tracking and testing means that Germany has, in comparison to other countries, a very low rate of undetected cases, which would obviously lead to a lower mortality rate. That's what the President of the RKI also said in todays press conference together with Angela Merkel.

Painy_: How big is the RKIs sample size tho?

patientzero_: All cases that had the flu and went to the hospital. So the more severe once. But they also re-ran the tests from the beginning of the year to test for Covid-19. If you can't detect it in there it wasn't in the country most likely

Sounds like a massive amount of testing that no other country can match.

For some context, researchers in China went back and reran old flu surveillance samples from Wuhan taken in December and the start of January. According to the WHO joint mission's report, 1 out of the 20 samples from the first week of January and 3 out of the 20 samples from the second week tested positive for Covid-19. China locked down Wuhan on the 23rd. Things were probably already really bad by that point in a way that wasn't reflected in the number of confirmed cases.

No matter good the test coverage in germany is, the growth is still exponential so the currect prevention measures are insufficient.

If the availability of testing kits is low and the ratio of infected to non infected people is extremely low, it makes absolutely no sense to sample randomly from the population.

How many do you need though? If you take 0.1-1% of your testing capacity, those handfuls of samples a day give you some information. Not regional level or very reliable data, but it gives an idea of whether people (as a population) are having it and are having mild symptoms and are not reporting anything, or if it isn't widespread yet and the hospital cases are the only cases.

Aldo if you expect the true positves to be a small percentage (which should still be the case in most countries), false positives will dominate in a ranom sampling. Apparently false positives are high for unsymptomatic cases. Of course if you can estimate the false positive rate well enough, the random sampling might still give useful statistics.

As far as I know lab performed PCR tests are assumed to have 0% false positives and about 29% false negatives. Antibodies tests have about 10% false-positive rate but to the best of my knowledge countries in Europe widely use PCR tests.

I think most places are switching from testing known contact/at risk countries to testing people in hospital with the symptoms. The first strategy makes sense if you're trying to contain a small number of cases, it doesn't make sense once people are catching it from other people in the area.