HUS (Haemolytic Uraemic Syndrome) Frequently Asked Questions

What is Haemolytic Uraemic Syndrome?
Haemolytic Uraemic Syndrome or HUS is serious syndrome (or collection of clinical features) consisting of a haemolytic anaemia (a low level of haemoglobin – the oxygen-carrying molecule in a red blood cell – caused by lysis or splitting open of the red blood cells), acute renal failure (where the kidneys fail to adequately filter waste products from the blood) and thrombocytopenia (a decrease in the number of platelets – blood-cell fragments that are important in the production of blood clots). When the red blood cells split open, the damaged cells and the free haemoglobin, block the kidneys leading to renal failure. HUS was first described in 1955; today it is most frequently associated with diarrhoeal infection caused by VTEC. HUS is the commonest cause of acute renal failure in children.  HUS is a notifiable condition in Ireland; it is reportable under the disease category of VTEC infection.

What causes HUS?
There are two forms of the disease: Infective HUS (also known as diarrhoea-associated HUS or D+HUS, as contrasted with the much rarer non-infective HUS (Also called D-HUS or atypical HUS) which is caused by a disorder of the body’s immune system. D+HUS is now recognised as a sequel to infection primarily with two gastrointestinal pathogens: VTEC and Shigella dysenteriae serotype 1 (S. dysenteriae type 1). VTEC is probably responsible for more than 95% of all cases of HUS seen in Ireland.

As well as VTEC and Shigella, very occasionally Campylobacter or HIV infection can result in HUS. Neuraminidase-producing organisms such as Streptococcus pneumonia and Clostridium butyricum very occasionally produce HUS. Non-infectious causes include drugs (contraceptive pill and cyclosporine), malignancy, post partum and idiopathic. The diarrhoeal form most commonly affects children under the age of five and, unlike the non-diarrhoeal, non-infectious form, is generally associated with recovery of renal function.

How does HUS develop?
If HUS develops following VTEC infection, it generally appears about seven days after the onset of the diarrhoea of VTEC (range 2-14 days).

How common is HUS in Ireland?
AS VTEC infection has become more common, so too has HUS; annually there are between 30 and 40 cases per year, with the majority of these in small children.

What are the clinical features of HUS?
As many as 95% of HUS cases follow VTEC infection. Anaemia and uraemia usually present with weakness, lethargy and sleepiness. Irritability in children may be a presenting feature. There may be purpuric areas (bruising) on the skin.

• Kidneys: microscopic haematuria (red blood cells visible only through a microscope) is common but gross haematuria can occur. Albuminuria is common, renal failure varies from mild to that requiring dialysis.
• Heart: diarrhoeal associated HUS patients have a normal blood pressure. Hypertension (high blood pressure) can occur in the non-infectious form with eye involvement including damage top the retina. Heart failure can occur particularly in women who have recently had a baby.
• Nervous System: damage to microvasculature (tiny blood vessels) can lead to developmental retardation in babies and small children and difficulty moving arms and legs. Convulsions are not uncommon.
• Gastrointestinal System: very occasionally perforation of the bowel due to microvascular ischaemic infarction (the wall of the bowel does not get enough blood due to damage to tiny blood vessels) and, in children, intussusception (obstruction of the small intestines).
• Skin: pallor (paleness) and purpura (bruising).
• General: fatigue, irritability, low/absent urinary output, swelling or arms, legs and face, and confusion.

What are the things I should look out for in my child?
The principal features of HUS are:

• Progressive failure to pass water (i.e. dry nappies)
• Generalised weakness (or floppiness in babies)
• Difficulty in rousing; sleepiness
• Pale face/skin
• Bruising
• Nosebleeds
• Swelling of face, wrists/hands, ankles/feet

If you see such features in your child, especially if they have been diagnosed with VTEC infection (or have diarrhoea, especially bloody) in the previous week, you should call your GP urgently. If you cannot contact your GP, you should take your child to your local hospital’s Emergency Department. Occasionally, HUS can develop as a result of VTEC infection that has not been identified (VTEC infection can be asymptomatic – there is no diarrhoea and the child may appear normal). Even if your child has had no preceding diarrhoea, if they develop some/any of the above symptoms, you should seek the advice of your GP.

How is HUS treated?
HUS is a medical emergency. Children who develop any of these symptoms should be admitted to hospital for specialist care. There is no specific treatment of HUS; antibiotics should be avoided for the VTEC infection.  The main danger to a child with HUS is lack of fluids. The first step will be to give the child intravenous fluids (through a drip), and to correct any imbalance in electrolytes (salts) in the blood. Sometimes, a child whose haemoglobin level is low may require transfusion (with blood, blood cells or platelets). Occasionally, while the child’s kidneys are recovering, s/he may require dialysis (removal of waste products from the blood). Rarely, the child may require plasmapheresis, in which as well as waste, antibodies and other harmful substances in the blood that may attach the body are also removed. 

What other investigations are likely?
As HUS is caused by VTEC infection, it will be important to determine where this infection may have come from. If your child develops HUS, as well as being looked after by clinical physicians in the hospital, you will be contacted by Public Health physicians who work in the community and who investigate VTEC cases to work out how your child may have acquired their infection and how far it may have spread. Stool samples may be requested from you and your children and you may be asked about your where you ate and what water you had consumed recently.

What is the outlook for HUS?
The outlook is excellent, especially in small children. Children under the age of five tend to recover rapidly. Occasionally children whose kidneys were damaged may require prolonged therapy such as dialysis. The outlook is not so good in elderly people; they have less of a reserve to fall back upon. Rapid intervention with fluids is crucial, so it is important to identify HUS as early as possible.

Last updated: 16 July 2014