Hemolytic Uremic Syndrome
Hemolytic uremic syndrome (HUS) is a poorly understood condition that affects the blood and kidneys. It usually follows an infection that has caused diarrhea.
What is going on in the body?
There are many causes for HUS. By far, the most common cause is an episode of diarrhea caused by infection with a particular strain of bacterium called E. coli.O157:H7. There have been a number of epidemics of HUS in recent years linked to eating undercooked beef containing this strain of bacterium. It 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 anemia, that is, low red blood cell 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. Between 0.3 and 10 per 100,000 children develop HUS in the U.S. each year. The condition tends to occur in epidemics.
What are the causes and risks of the condition?
The most common cause of HUS is the bacterium known as E. coli O157:H7.
Less common causes of this condition include:
- other bacteria and viruses
- inherited factors
- certain medications
- organ transplants, such as heart transplant, liver transplant, pancreas transplant, or lung transplant
- certain types of cancer
In some cases, there is no obvious cause for the illness.
Several factors put a person at risk for acquiring the diarrhea-related form of HUS. These cases are due to contamination of the substance with the special strain ofbacteria. Examples of substances that may be contaminated include:
- raw or undercooked beef
- unpasteurized 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.
What can be done to prevent the condition?
Diarrhea-related HUS can be prevented by:
- cooking all meat well. A person should avoid meat prepared "rare". Cooking meat to an internal temperature of at least 160 degrees Fahrenheit 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 unpasteurized milk and fruit juice
- washing hands thoroughly and disinfecting diaper-changing surfaces after changing diapers, especially if the child has diarrhea
- being careful not to swallow water when swimming in lakes or ponds, especially around farmland
How is the condition diagnosed?
HUS is often suspected after the history and physical exam. A complete blood count, (CBC) can identify low platelet counts or low red blood cell counts, known as anemia. Kidney function tests can detect kidney damage.
Long Term Effects
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 behavior.
What are the risks to others?
Most of the bacteria and viruses that cause HUS can be passed to other people. E. coli O157:H7, for example, remains in the feces of infected people for a week or two after the diarrhea clears up.
What are the treatments for the condition?
A person with HUS often requires admission to the hospital. Treatment may include:
- 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.
What are the side effects of the treatments?
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 CBC, and kidney function tests.