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E. coli is one of the most virulent (highly infectious) pathogens known to enter the world food supply. 

Symptoms

It causes 

The initial symptoms of E. coli illness generally occur within two days after eating contaminated food, though three to five days have been reported. Symptoms increase in intensity during the next 24-48 hours, lasting from four to 10 days. 

Hardiness of E. Coli

Less than ten E. coli cells may be enough to cause foodborne illness in humans. A low infectious dose of two to 2,000 cells has been associated with outbreaks. E. coli can survive in acidic environments that are lethal to other pathogens, such as in fermented foods like sausage and apple cider. Though potentially deadly to humans, E. coli is not pathogenic to cattle. A single cow, or cattle within the same herd, may contain more than one strain of E. coli. Some strains are thought to have greater acid tolerance than others. 

How Does it Spread?

The source of E. coli contamination on carcasses is likely due to fecal contamination during animal production and slaughter operations. Carcasses may become contaminated during hide removal or by cross-contamination with equipment and workers' hands. HACCP systems in processing plants cannot eliminate E. coli from foods unless a treatment is added that will kill the pathogen, such as heat pasteurization or irradiation. Current research shows that competitive exclusion has the potential to eliminate E. coli from cattle before slaughtering. Competitive exclusion involves the use of non-pathogenic microorganisms to outgrow pathogens in the gastrointestinal tracts of animals. If swallowed, fecally contaminated water in freshwater swimming areas may cause E. coli infection in both cattle and humans. Fresh manure used to fertilize garden fruits and vegetables may contaminate them with E. coli. The largest reported E. coli O157:H7 outbreak, which caused thousands of illnesses, occurred in Japan in 1996. Radish sprouts were implicated as the source of infection.