Infections by flesh-eating bacteria are rare. The affliction can destroy muscle, fat and skin and may require surgery to remove the diseased tissue to save a patient's life.
Hanneman had several operations to remove dead and dying tissue from his arm, the band said on its website last year.
It's unknown if Hanneman was bitten by the dangerous brown recluse spider. Robinson-Fitzgerald said the spider that bit the Slayer guitarist was never recovered.
The government estimates roughly 750 flesh-eating bacteria cases occur each year, usually caused by a type of strep germ. About 1 in 5 people with the most common kind of flesh-eating strep bacteria die.
People with weakened immune systems can be more at risk.
Flesh-eating bacteria, by itself, doesn't cause liver failure. But at least one type of strep bacteria can cause streptococcal toxic shock syndrome, which can lead to liver failure.
It is unclear whether an autopsy will be scheduled. No funeral arrangements have been made.
"Jeff Hanneman will always be a metal god," rocker Andrew W.K. posted on Twitter.
Hanneman co-founded the thrash metal pioneers in Huntington Beach, California, in 1981.
- AP