E. coli O157:H7 is one of hundreds of strains of the bacterium E. coli. Although most strains are harmless and live in the intestines of healthy humans and animals, this strain produces a powerful toxin and can cause severe illness.
A rare but dangerous type of E. coli, the strain O157:H7 is now a major public health problem worldwide.
Infection often causes severe bloody diarrhea and abdominal cramps; sometimes the infection causes non-bloody diarrhea. Frequently, no fever is present. It should be noted that these symptoms are common to a variety of diseases, and may be caused by sources other than contaminated drinking water.
In an estimated 4 percent of cases, E. coli O157:H7 produces shiga toxin that attacks the lining of the intestine and enters the blood stream, causing hemolytic uremic syndrome or HUS, which can lead to kidney failure, anemia, internal bleeding and other complication, including death.
In some people, particularly children under 5 years of age and the elderly, the infection can also cause a complication called hemolytic uremic syndrome, in which the red blood cells are destroyed and the kidneys fail.
The capacity of E. coli O157:H7 to cause disease is a direct result of its possession of a number of genetic elements for virulence factors. Due to the severity of O157:H7 infection, research into the virulence factors has been intense.
In the United States, hemolytic uremic syndrome is the principal cause of acute kidney failure in children, and most cases of hemolytic uremic syndrome are caused by E. coli O157:H7. Hemolytic uremic syndrome is a life-threatening condition usually treated in an intensive care unit. Blood transfusions and kidney dialysis are often required. With intensive care, the death rate for hemolytic uremic syndrome is 3%-5%.
The effects of E. coli O157:H7 on human health
