Outbreaks Caused by Non-O157 Shiga Toxin-Producing E. coli
Worldwide, non-O157 STEC outbreaks began being recognized in the 1980s, and the first reported outbreak in the United States occurred in 1990.
Prior to 2000, only four non-O157 STEC outbreaks were identified in the United States, two of them in 1999. From 2000 through 2010, more than 40 non-O157 STEC outbreaks were identified. Almost half of them were foodborne, but many were due to person-to-person transmission, particularly in child daycare settings. Occasional outbreaks were due to waterborne transmission or contact with ruminant animals (e.g., calves, goats) in public animal contact settings. To date, food sources of non-O157 STEC outbreaks have generally been very similar to those for E. coli O157, including ground beef, leafy greens, sprouts, raw milk, raw flour, bison, and venison (https://www.cdc.gov/ecoli/outb...). Transmission from contact with ruminant animals or their environments at venues like petting zoos and fairs is also important.
An extraordinary, devastating outbreak occurred primarily in Germany beginning in May 2011. The E. coli serotype involved was E. coli O104:H4. While technically a STEC (because it produced Shiga toxin), this pathogen was not a typical STEC strain; rather, it was a hybrid between STEC and the diarrheagenic pathotype known as enteroaggregative E. coli (EAEC). It was also extremely virulent. Ultimately, the outbreak sickened over 4,300 people, caused 852 cases of HUS, and killed more than 50 people, primarily previously healthy young adult females. Part of the extreme virulence of this strain can be attributed to the fact that it possessed the Shiga toxin 2a variant, which is the most common variant associated with HUS. However, this strain also possessed additional virulence factors not typically found in STEC strains. The disproportionately large involvement of adult women was likely due to the outbreak vehicle – sprouts grown from fenugreek seeds from Egypt. This outbreak was the most spectacular and terrifying example of the emergence of hybrid or unusual strains of STEC that have increased ability to cause severe disease. This increasingly recognized phenomenon results from the ability of different pathotypes of diarrheagenic E. coli to acquire virulence factors from other E. coli strains when they co-infect the intestines of animals or people.
Other examples of E. coli outbreaks are included below: