E. coli O157:H7 was identified for the first time at the CDC in 1975, but it was not until seven years later, in 1982, that E. coli O157:H7 was conclusively determined to be a cause of enteric disease. Following outbreaks of foodborne illness that involved several cases of bloody diarrhea, E. coli O157:H7 was firmly associated with hemorrhagic colitis.
The Centers for Disease Control and Prevention (CDC) estimated in 1999 that 73,000 cases of E. coli O157:H7 occur each year in the United States. Approximately 2,000 people are hospitalized, and 60 people die as a direct result of E. coli O157:H7 infections and complications. The majority of infections are thought to be foodborne-related, although E. coli O157:H7 accounts for less than 1% of all foodborne illness.
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 bacteria.
While the majority of foodborne illness outbreaks associated with E. coli O157:H7 have involved ground beef, such outbreaks have also involved unpasteurized apple and orange juice, unpasteurized milk, alfalfa sprouts, and water. An outbreak can also be caused by person-to-person transmission of the bacteria in homes and in settings like daycare centers, hospitals, and nursing homes.
Symptoms of an E. coli O157:H7 Infection
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 naked eye. Vomiting can also occur, but there is usually no fever. The incubation period for the disease (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 intestinal illness lasts about a week and resolves without any long-term problems.
Complication of an E. coli O157:H7 Infection
Hemolytic Uremic Syndrome (HUS) is a severe, life-threatening complication of an E. coli O157:H7 bacterial infection. Although most people recover from an E. coli O157:H7 infection, about 5-10% of infected individuals goes on to develop HUS. E. coli O157:H7 is responsible for over 90% of the cases of HUS that develop in North America. Some organs appear more susceptible than others to the damage caused by these toxins, possibly due to the presence of increased numbers of toxin-receptors. These organs include the kidney, pancreas, and brain.
Thrombotic Thrombocytopenic Purpura (TTP) is a clinical syndrome defined by the presence of thrombocytopenia (low blood platelet counts) and microangiopathic hemolytic anemia. This has generally been recognized as “adult HUS.” There are many possible causes, including E. coli O157:H7, all of which act through the common mechanism of inducing endothelial cell damage. The damage triggers a cascade of biochemical events that ultimately leads to the characteristic feature of TTP – widespread dissemination of hyaline thrombi, composed predominantly of platelets and fibrin, which block the terminal arterioles and capillaries (microcirculation) of most of the major body organs, commonly, the heart, brain, kidneys, pancreas and adrenals. Other organs are involved to a lesser degree. The pathophysiology of this disease results in multisystem abnormalities and the clinical manifestations of the syndrome.