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Haemolytic uremic syndrome is a poorly understood condition that affects the blood and kidneys. It usually follows an infection that has caused diarrhoea.
What is going on in the body?
There are many causes for HUS. By far, the most common cause is an episode of diarrhoea caused by infection with a special strain of the bacterium, E. coli. There have been a number of epidemics of HUS in recent years linked to eating undercooked beef containing this strain of bacterium. This bacterium produces a toxin that is very harmful to cells, particularly those of the kidneys, blood vessels, and intestinal lining. There are other less common causes of HUS in which the exact cause is not as clear.
HUS is thought to develop when the lining of small blood vessels become damaged. This most commonly occurs in the blood vessels that supply blood to the kidney. The damage causes the blood vessels to swell. Tiny blood clots can form in affected blood vessels, narrowing the vessels or blocking them completely. Because blood cannot pass through these blocked or narrowed vessels, the kidneys are less able to filter waste products from the body and may become damaged. Certain cells in the blood, such as red blood cells that carry oxygen and platelets that help clot the blood, are damaged as they try to pass the narrowed vessels. This leads to anaemia, or low blood counts, and poor clotting ability.
Most cases of HUS affect infants and young children between the ages of 7 months and 4 to 6 years. The condition tends to occur in epidemics.
What are the signs and symptoms of the condition?
The primary symptoms of HUS include:
Other symptoms are related to the underlying cause. For example, some cases are related to pregnancy, in which case diarrhoea may not occur.
- diarrhoea. This may be profuse and watery, and is often bloody. It may be accompanied by vomiting and abdominal distress. At first the condition may resemble the stomach flu, but then the child becomes very ill. Later symptoms include lethargy, irritability and paleness.
- decreased urine output, due to kidney damage. There may also be signs of fluid retention in the body. These may include swelling of the extremities and eyelids, shortness of breath, and high blood pressure.
- bleeding. A large amount of bleeding is rare. However, small quantities of blood may ooze from the puncture site when blood is drawn for testing. A flat rash of red or purple dots, called petechiae, may appear. The person may also have large areas of bruising.
- brain disfunction, which is more common in types of HUS not linked to diarrhoea. This may cause irritability, lethargy, cognitive impairment, coma, seizures, and brain swelling.
What are the causes and risks of the condition?
The most common cause of HUS is the special strain of E. coli bacteria, called E. coli 0157:H7.
Less common causes of this condition include: In some cases, there is no obvious cause for the illness.
Several factors put a person at risk for acquiring the diarrhoea-related form of HUS. These cases are due to contamination of the substance with the special strain of E. coli bacteria. Examples of substances that may be contaminated include:
What can be done to prevent the condition?
- raw or undercooked beef
- unpasteurised milk or fruit juice, especially apple juice
- contaminated water. This is common in underdeveloped countries without proper water treatment, or lakes and ponds near farms that either have cattle or use manure.
Diarrhoea-related HUS can be prevented by:
How is the condition diagnosed?
- cooking all meat well. A person should avoid meat prepared "rare". Cooking meat to an internal temperature of at least 71 degrees Celsius is advised.
- washing hands, cutting boards, knives and plates used to prepare raw meat in hot, soapy water. This should be done before these items come in contact with other food or utensils.
- avoiding unpasteurised milk and fruit juice
- washing hands thoroughly and disinfecting nappy-changing surfaces after changing nappies, especially if the child has diarrhoea
- being careful not to swallow water when swimming in lakes or ponds, especially around farmland
HUS is often suspected after the history and physical examination. A full blood count, or FBC, can identify low platelet counts or low red blood cell counts, known as anaemia. kidney function tests can detect kidney damage.
What are the long-term effects of the condition?
HUS sometimes causes permanent loss of kidney function, and sometimes even kidney failure. However, roughly 50 to 80% of people with this condition recover fully.
There is also a mild risk of brain damage in some cases. This may result in serious long-term problems, such as seizures, paralysis, or changes in personality or behaviour.
What are the risks to others?
Most of the bacteria and viruses that cause HUS can be passed to other people. E. coli, for example, remains in the faeces of infected people for a week or two after the diarrhoea clears up.
What are the treatments for the condition?
A person with HUS often requires admission to the hospital. Treatment may include:
What are the side effects of the treatments?
- fluids and salt given through an IV tube in the arm
- medications, such as diuretic medications or "fluid pills," to promote urination. Medications to treat high blood pressure, which commonly occurs when the kidneys are damaged, may also be needed.
- use of dialysis if the kidneys stop working. Dialysis is a procedure in which the person is hooked up to a machine to filter the blood. Dialysis may be needed for a long period of time or even permanently in severe cases. Some people may ultimately need a kidney transplant.
- blood transfusion of red blood cells or platelets if the blood counts get too low. Other blood products may be needed in special circumstances.
All medications have possible side effects, such as allergic reactions, stomach upset, and others. Specific side effects depend on the medications used. Transfusion of blood products may cause allergic reactions or infections in some cases. Dialysis is a complicated treatment that has to be done often. There are many possible side effects, including death.
What happens after treatment for the condition?
Kidney function may be slightly lower even in someone who seems to have recovered fully. The long-term effects of this are unclear. Many people can return to normal activities shortly after recovery. Those with severe kidney damage may require ongoing treatment for life.
How is the condition monitored?
A person who has had HUS is often monitored regularly with full blood counts, or FBC's, and Kidney function tests.
Author: John Wegmann, MD
Reviewer: eknowhow Medical Review Panel
Editor: Dr John Hearne
Last Updated: 19/06/2005
Potential conflict of interest information for reviewers available on request