The bacterium was first identified by the Centers for Disease Control and Prevention (CDC) in 1975, but was not conclusively determined to be a cause of enteric disease until 1982, following outbreaks of foodborne illness that involved several cases of bloody diarrhea. At that time, E. coli O157:H7 was firmly associated with hemorrhagic colitis. The majority of infections are thought to be food-related, although E. coli O157:H7 accounts for less than one percent of all food poisoning cases.
E. coli O157:H7 bacteria are believed to mostly live in the intestines of cattle but have also been found in the intestines of chickens, deer, sheep, goats, and pigs. E. coli O157:H7 does not make the animals that carry it ill; the animals are merely the reservoir for the bacterium.
While a large number of foodborne illness outbreaks associated with E. coli O157:H7 have involved ground beef, such outbreaks have been increasingly associated with fresh produce, such as lettuce and spinach, but outbreaks have also been traced to unpasteurized apple and orange juices, raw milk, alfalfa sprouts, and water. Person-to-person transmission of the bacterium has been documented in homes, hospitals, daycare centers, nursing homes and many other locations.
E. coli O157:H7 infection 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 the naked eye. Vomiting, and rarely fever, can also be symptoms. The incubation period for the illness (the period from ingestion of the bacterium to the start of symptoms) is typically three to nine days, although slightly 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 intestinal illness lasts about a week and resolves without any long-term problems.
Although most people recover from E. coli O157:H7 infection, about five to ten percent of infected individuals develop hemolytic uremic syndrome (HUS), a severe, life-threatening complication of E. coli O157:H7 bacterial infection. HUS develops when E. coli’s toxins enter the circulation by binding to special receptors. During HUS, red blood cells are destroyed and cellular debris accumulates within the blood vessels while the body’s clot-breaking mechanisms are disrupted, causing blockage of the terminal arterioles and capillaries (microcirculation) of most of the major body organs, commonly the heart, brain, kidneys, pancreas and adrenals.
E. coli O157:H7 is responsible for over 90 percent of the cases of HUS that develop in North America. Some organs appear more susceptible than others to the damage caused by these toxins. These organs include the kidney, pancreas, and brain.
Some patients suffering from E. coli and HUS are diagnosed with Thrombotic Thrombocytopenic Purpura (TTP), a clinical syndrome defined by the presence of thrombocytopenia (low blood platelet counts) and microangiopathic hemolytic anemia. It is sometimes called “Adult HUS”.
Contact your health care provider if you believe you have become ill with an E. coli infection.
Infection with E. coli O157:H7 is usually confirmed by detecting the bacterium in the stool of an infected individual through laboratory testing.
Antibiotics do not improve the illness, and some medical researchers believe that medications can increase the risk of complications. Therefore, apart from good supportive care, such as close attention to hydration and nutrition, there is no specific therapy for the treatment of E. coli O157:H7 infection. The recent finding that a toxin produced by 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.