After someone ingests a sufficient quantity of E. coli O157:H7, the bacteria travels through the stomach and small intestine, and then attaches itself to the inside surface of the large intestine and causes inflammation of the intestinal wall. This inflammatory reaction is caused by toxins secreted by the bacteria, and is believed to be the cause of hemorrhagic colitis.8,9
Hemorrhagic colitis, the first E. coli symptom, is characterized by the sudden onset of abdominal pain and severe cramps, followed within 24 hours by diarrhea. As the disease progresses, the diarrhea becomes watery and then may become grossly bloody – bloody to naked eye. E. coli symptoms sometimes include vomiting, but rarely fever. The incubation period for E. coli O157:H7 infection (i.e., the period from ingestion of the bacteria to the start of symptoms) is typically 3 to 9 days, although shorter and longer periods are not that unusual. An incubation period of less than 24 hours would be unusual, however.

In most infected individuals, the E. coli symptoms last about a week and resolve without any long term problems. Antibiotics do not improve the illness, and some medical researchers believe that these medications can increase the risk of complications.10 Therefore, apart from good supportive care, such as close attention to hydration and nutrition, there is no specific therapy to halt E. coli symptoms. However, the recent finding that toxin E. coli O157:H7 initially greatly speeds up blood coagulation may lead to medical therapies in the future that could forestall the most serious consequences.11 Most individuals recover within two weeks.
8. Tarr PI. Escherichia coli O157:H7: Clinical, Diagnostic, and Epidemiological Aspects of Human Infection. Clinical Infectious Diseases 1995;20:1-10.
9. Boyce TG, Swerdlow DL, Griffin PM. Escherichia coli O157:H7 and the hemolytic-uremic syndrome. New England Journal of Medicine, 1995;333:364-368.
10. Wong CS, Jelacic S, Tarr PI. The risk of the hemolytic uremic syndrome after antibiotic treatment of Escherichia coli O157:H7 infections. N Engl J Med, 2000; 342:1930-36.
11. Chandler WL, Tarr PI, et al. Prothrombotic Coagulation Abnormalities Preceding the Hemolytic-Uremic Syndrome. N Engl J Med, 2002; 346: