They did. They tested a lot of people in contact with infected people (so even more likely to be an asymptomatic carrier than the general population) and their findings from the link above is:
> Asymptomatic infection has been reported, but the majority of the relatively rare cases who are asymptomatic on the date of identification/report went on to develop disease. The proportion of truly asymptomatic infections is unclear but appears to be relatively rare and does not appear to be a major driver of transmission.
Given the evidence the onus is proof is now on anyone claiming there are large amounts (of course there will always be some) of undetected cases.
I think what you may be missing is that 100,000 people in WA could have gone to their doctor last week with “a cold” and they wouldn’t have been tested for COVID, because the FDA would not allow state labs to run the tests and the CDC refused to run it on mild cases.
I use the example of WA because it’s glaringly obvious that a lack of testing has resulted in a significant number of cases going undetected over the last couple weeks in that area.
The old CDC guidelines only allowed severe cases to be tested, so the only confirmed COVID cases were severe. Resulting in a “fatality rate” that was pushing 10%.
So it’s just an example of how this number is inflated by lack of testing. I believe a similar situation is playing out in Italy.
By comparison, South Korea has an extremely robust testing regime (free drive through testing stations, over 100,000 tested, capacity of over 10,000 per day) [1] and has identified 6,284 cases and has seen 40 deaths with currently 52 in serious condition. That puts their “known case fatality rate” at 0.6%-1.5%.
Simply put, the “known case fatality rate” can only possibly overstate the actual fatality rate, unless you believe there are deaths due to COVID happening that are being misattributed. This is obviously an entirely different category of error than not testing someone with a mild cold.
It’s useful to take what we know about “known case fatality rate” in heavily-tested populations and we can use this to estimate how many undetected cases are present in the population in under-testing locales. E.g. 10 COVID deaths would point to the likelihood of over 1,000 actual cases of COVID in the community. This of course assumes similar demographics and standards of care, which may not be the case.
[1] - https://www.ctvnews.ca/health/south-korea-takes-fast-food-ap...
There is definitely under reporting of cases (and some misdiagnosed deaths), but so far no reason to think it's a tip of an iceberg type of scenario and there are large masses of undiagnosed people. For calculating mortaility rates there's also the lag time between getting the virus and death to take into consideration.
Going back to your original post about the fatality rate in WA, the numbers are simply too low to indicate anything at all. There are only 4 countries on Earth we can get much statistical significance from and of those Iran is the only one that lacks testing at the moment.
Once that’s negative you would expect maybe a COVID test would be done, again, depending on the health care system, availability of testing, and perhaps the financial impact.