https://nltimes.nl/2020/04/16/3-dutc...-19-antibodies
The primary source mentioned in the article is in Dutch, so if anyone can translate and find more information it would be helpful. Would love to know which test they used and the sensitivity/specificity of it. Blood donation is not fully representative of population as it excludes the very young and very old.
But if 3% of non-cases have antibodies and around the midpoint of the study there were 20,000 cases diagnosed.
https://www.worldometers.info/corona...y/netherlands/
3% of a population of 17 million is 510,000 infections for those 20,000 cases or a
25x multiplier of cases to estimate infections.