There are two main sources for formula milk to be contaminated by Enterobacter sakazakii:one is that the milk powder  contains a small amount of Enterobacter sakazakii; the other is to enter the formula through the surrounding environment and bacteria-contaminated equipment or hands.
Water above 70 degrees Celsius can kill Enterobacter sakazakii.
 the World Health Organization recommends that no less than 70 degrees Celsius of water to prepare infant formula.