Mortality rate
Until the past 15 years or so, the mortality rate was consistently
reported as well over 50%.3 However, all of these reports comprised
individual cases or case series in which doctors collected cases and then
reported characteristics of the population. As noted before, case series
typically have problems with ascertainment bias. Specifically, the
reported cases in no way reflect a random sample of the disease population.
As is obvious, case series tend to collect the sickest patients with
the worse outcomes—conditions necessary to make the patients worth
the effort of reporting in the first place.