The common/normal e.coli is not all that 'bad' a bug. A few are now known (recent years) to be quite vicious. E. coli has historically been used (& will continue to be) as an INDICATOR bacteria, indicating fecal contamination-which contains various types of VICIOUS and DEADLY micro-organisms. NOT just to the immuno-compromised individual, but to EVERYONE!!
I could list the extensive possibilities of illnesses and diseases (some FATAL) of food/water fecal contamination, but if you care, google it.

gimpy