E. Coli O157:H7 infects 75,000 people per year in the United States and is responsible for an estimated 3 percent of acute foodborne illnesses. It’s ability to cause bloody diarrhea, kidney failure, and death makes it much feared. Most cases are caused by eating contaminated, undercooked ground beef or swimming in or drinking water contaminated by human sewage. However, an increasing number of cases involve contaminated vegetables (such as lettuce and broccoli) as well as person-to-person contact.
E. Coli O157:H7 & the Shigella Toxin
E. Coli O157:H7 is one of hundreds of strains of the Escherichia coli, a bacteria that normally lives harmlessly in the gut. The O157:H7 refers to specific markers found on its surface, which are used to distinguish it from other types of E. coli. What makes E. Coli O157:H7 different than ordinary E. Coli is its ability to produce a powerful toxin called the Shigella toxin.The Shigella toxin attacks the lining of blood vessels thus leading to significant damage and bleeding. It primarily affects the small vessels in the digestive tract and kidneys but it can affect the lung and nervous system as well. When it attacks the gut it can lead to bloody diarrhea (enterohemorrhagic). When it triggers more widespread damage (particularly the kidneys), it is called hemolytic-uremic syndrome (HUS).
Enterohemorrhagic E. Coli (EHEC)
Not every infection with E. Coli O157:H7 (or other types of E.Coli capable of producing the Shigella toxin) leads to the bloody diarrhea. For many people, the E. Coli O157:H7 infection only cause watery diarrhea. However, when it happens, the severe abdominal pain and bloody diarrhea can be dramatic. The highest rate of infection rates occurs in children under age 5 and the elderly.EHEC is diagnosed by finding E. Coli O157:H7 (or a similar E. Coli) in the bloody stools. Treatment is primarily supportive as antibiotics and anti-toxins haven’t been shown to be consistently helpful (in fact they may make things worse). Fortunately, uncomplicated infections resolve in about a week and most people recover without any long-term complications.
Hemolytic-Uremic Syndrome (HUS)
The most concerning complication of EHEC is hemolytic-uremic-syndrome (or HUS). This occurs when the Shigella toxin causes blood clots to form in the small blood vessels of various organs, particularly the kidneys. HUS diagnosed when there is signs that these blood clots are consuming platelets (thrombocytpoenia), chewing up red blood cells (hemolytic anemia), and causing kidney damage (acute kidney failure).HUS complicates between 5-10% of EHEC cases and typically occurs 5-10 days after the start of the diarrhea. Once EHEC is recognized, attempts to prevent progression to HUS are generally unsuccessful. Treatment primarily involves supportive therapy such as blood transfusions for severe anemia or dialysis for kidney failure. Fortunately, HUS resolves within 1-2 weeks and the prognosis is generally excellent. However, a small number of people (5%) develop lasting kidney failure, strokes or death.
Kidney Failure
As many as 50% of those with HUS will require develop acute kidney failure requiring dialysis. In fact, it is now recognized that HUS is one of the main causes of acute kidney failure in children. For most (>95%), the kidney failure resolves, kidney function appears to return to normal and dialysis can be discontinued. However, long term monitoring for unrecognized but irreversible kidney injury is prudent.For an unlucky few (< 5%), the kidney failure does not resolve and end-stage kidney disease is diagnosed. This means dialysis will have to continue after HUS has resolved. Kidney transplantation is an excellent option for children with permanent kidney failure. Reoccurrence of HUS after a kidney transplant is extremely uncommon.
Sources
- Stephen Calderwood, MD. Clinical manifestations, diagnosis, and treatment of enterohemorrhagic Escherichia coli. UpToDate [online]. Accessed on September, 18, 2006.
- Patrick Niaudet, MD. Treatment of typical hemolytic uremic syndrome in children. UpToDate [online]. Accessed on September, 18, 2006.