98,000 deaths by medical errors every year - 2008 article

https://www.massnurses.org/news-and-events/archive/2008/p/openItem/973

"Kumar says he wrote the book to alert the public to the fact that
98,000 patient deaths occur as a result of medical errors in U.S.
hospitals annually, and about half of them are preventable."

are they saying that 50K deaths from errors are NOT preventable? what
kind of errors are NOT preventable?