Completely avoidable by roasting the peanuts according to spec. This guy cut corners big time.
http://www.nutritionalanarchy.com/2014/08/13/heres-why-and-how-you-should-make-your-own-peanut-butter/
Peanut producers use roasters to kill any Salmonella that might be lingering on raw peanuts, but the process requires roasting at a high enough temperature for a long enough time. Gray discovered that Peanut Corp. was not following the correct protocol – instead of monitoring the roasting process, they simply relied on the peanuts turning a certain color.