They use to be. The institute though is not that brilliantly dealing with possibilites, in my view. To have proper facts as much as possible:
Streeck et al presented their preliminary results with already a sample size of 509 in a high hit area. 500, I think, is already two times as high as the WHO considers to be needed for a proper evaluation.
PCR (reflecting acute infection) - 2%
antibody test* (reflecting past infection) - 14%
case fatality - 0.37%
mortality - 0.06%
They didn´t explain how they evaluated the mortality, wether from excess mortality in this very area (as usually done with flu mortality) evaluating local empirical data, or from their other results. The latter is more likely, I would think. In this case the mortality should turn out to be even lower, because for a case that has died counts probably Anyone who tested positive and has died, regardless of other risks and causes which uses to lead to death someday and maybe this month.
Yesterday in Dutch TV the news said that there is a higher mortality observed in the last month, presumably coming from corona deaths "which havn´t been diagnosed and died at home". Unfortunately they didn´t give any percentage.
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*Gold standard to the antibody test is probably the PCR test (which hopefully is accurate enough). There is no principal problem to use an antibody test (in an epidemiological study). The average of other coronaviruses in acute infection is 7-15%, so there shouldn´t be that much of inaccuracy possible anyway (so mainly mistakes coming from a range of 8%). - If one finds it worth one could even estimate the inaccuracy of the antibody test for each village, town or country newly, and/or for each time of investigation. A PCR is not expensive and not too difficult to do (one only needs to wait until the known positives from the PCR tests shall show antibodies).
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@Snow Leopard, it took me some time to relearn this, and better deleted two other posts)
