i wish more countries did randomized testing over its whole population, or extensive testing, like SK.

Why even test? The decision procedure is the same: treat the ill, lock down everyone else at home, avoiding social contact at the max; enforce social isolation and/or masks in "critical" spaces (power plants, grocery stores, ...). What does a positive or negative test change?

Most complete lockdown would seem to coincide with health care system stress beyond a certain level.

Universal testing and full identification, isolation, and clearance of all patients across multiple checkpoints would result in the fewest number subject to confinement, confined in the least broad of areas for the shortest periods of time.

OTOH if insignificant testing has been achieved, lockdown itself will need to be inversely universal and long-lasting.

There is an exponential component involved, so the effect will be felt sooner than you think.

Theoretically either way, it's possible no one will be able to be unconfined across multiple checkpoints without a real-time valid negative test or credential.

That decision could be the same either way.

But the fewer and less reliable the tests, the fewer the number of citizens that can be expected to be allowed to move about with some freedom.

After pandemic stress exceeds the magnitude where there can be no treatment resources for additional patients anyway, movement will certainly not be relaxed, and those who might have had a chance with earlier & more thorough action & testing will be left to expire undertested in confinement.

Not every scenario is that uplifting.

Due to the excess rate of confinement resulting from inadequate testing, the greater stress on the marginal economic needs of a large contingent of the populace may result in a need for lockdowns to become oppressive enough to theoretically halt the spread of all possible crime in addition to disease.

Depends on how serious it gets, if it's bad enough you could get unrulyness or looting like there is during some disasters regardless.

How do we know when to initiate or let up on the lockdown if we don’t have any testing?

For the first question, the answer is: ANY country that currently is seeing exponental growth should take action at the same level of severity as China/Korea/Singapora, if not, they will be in the same situation as Italy in 1-3 weeks.

Once the growth is no longer exponential, measures can be rolled back slowly, especially if they have access to enough tests, masks and respirators.

The earlier action is taken, the cheaper it will be to stop this. Every week of delay can increase casualty rates by a factor of 10. A month of delay, can mean the difference between 10000 and 10 million dead.

Also, economic costs, both in direct treatment cost as well as the disruption to the productive side of the economy will rise sharply the longer we wait. (Well, at least if we don't see the death of sick and elderly as an economic benefit.)

A decline in cases to treat would be informative, no?

You're assuming that all cases are Coronavirus.

People will continue to get the Flu, Colds, HIV / AIDs even throughout this whole shebang. We need to know COVID19 cases specifically, to know if our lockdown methodology is being effective.

For that you just need to test in hospitals.

USA doesn't have enough tests even for that. I'm proposing we at least test the cases that reach the hospital stage.

Exactly. I don't see how trying to limit testing to people who had contact with known cases or traveled to at risk countries (as practiced in Germany) can be successful.

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.

Everyone except the UK and the US notably.