First, it should be pointed out that Escherichia coli (E.coli) is a bacteria that normally lives in the intestines of both people and animals. In all actuality, most forms of E.coli are harmless and are considered an important part of the human intestinal tract. The other types of E.coli are considered pathogenic, meaning they can cause illness.
The most popular form of pathogenic E.coli, as most commonly heard about in news reports are the "Shiga toxin-producing E.coli" or STEC (these can also be referred to as Verocytotoxin-producing E.coli (VTEC) or Enterohemorrhagic E.coli (EHEC). The most common of these types of E.coli is the E.coli O157:H7.
E.coli O157 was first identified as a pathogen in 1982. Unfortunately, non-O157 E.coli are not nearly as well understood, partially because foodborne illness outbreaks are rarely reported or identified. Even though these non-O157 forms are less well known, it is still extremely important to follow proper food safety procedures to minimize the chances of exposure to these pathogens, as some of the non-O157 groups can cause the most severe manifestations of STEC illnesses.
More information on E.coli can be found at the CDC:http://www.cdc.gov/ecoli/general/