Bacillus cereus are bacteria that cause serious illness in humans. Many cases of illness related to Bacillus cereus are caused by eating contaminated foods.
The recent tragic cases involving babies in neonatal units are extremely unusual, as it appears the infections were through intravenous fluids given as nutrition to the babies. This meant that the bacteria entered the blood stream of these already vulnerable babies directly, with tragic results.
An investigation is now underway to determine how the Bacillus cereus got into the intravenous, but it would appear from this statement by Public Health England that this was down to an isolated incident in the strictly controlled manufacturing process.
Bacillus cereus is commonly found in the environment, hence the need for the strictest conditions during production to keep harmful bacteria out.