Hemolytic Uremic Syndrome (HUS)

What happens in HUS

In typical HUS, E. coli bacteria in the gut release Shiga toxin, which enters the bloodstream and damages the lining of small blood vessels, particularly in the kidneys. This triggers:

1. Tiny clots in small vessels (thrombotic microangiopathy)
2. Hemolytic anemia: red blood cells are shredded as they squeeze past the clots
3. Low platelets (thrombocytopenia): platelets are used up in the clots
4. Acute kidney injury: the kidney filters are damaged, so urine output falls and waste builds up

The brain, heart, pancreas and other organs can also be affected.

Causes and types

How people get STEC

• undercooked ground beef
• unpasteurized (raw) milk, juice or cheese
• contaminated raw vegetables such as lettuce, spinach and sprouts
• contaminated water, including lakes and pools
• petting zoos and farm animals
• person-to-person spread, especially in childcare settings

Symptoms

The diarrheal phase

E. coli infection begins 3 to 4 days after exposure with stomach cramps, vomiting and diarrhea that often becomes bloody within 1 to 3 days. Fever is usually low or absent.

Signs of HUS

HUS typically develops about 5 to 10 days after diarrhea starts, often as the diarrhea is improving:

• peeing less often or not at all
• pale skin, including the inside of the lower eyelids
• tiredness and irritability
• unexplained bruises, tiny red spots or bleeding from the nose or mouth
• swelling of the face, hands, feet or body
• high blood pressure
• confusion, seizures or drowsiness in severe cases

Diagnosis

• Blood count: low hemoglobin and low platelets
• Blood smear: fragmented red blood cells (schistocytes)
• Markers of hemolysis: high LDH, low haptoglobin, raised bilirubin
• Kidney tests: creatinine and electrolytes
• Urine tests: blood and protein
• Stool testing: for Shiga toxin and E. coli O157
• Complement studies and genetic tests if atypical HUS is suspected
• ADAMTS13 test to rule out thrombotic thrombocytopenic purpura (TTP), which looks similar

Treatment

There is no specific cure for typical HUS; treatment supports the body while it recovers:

• Hospital care, often in a pediatric kidney unit
• Careful IV fluids early in the illness, which may protect the kidneys
• Red blood cell transfusions for severe anemia
• Platelet transfusions only for bleeding or before procedures
• Dialysis: about half of children with HUS need temporary dialysis
• Blood pressure control and nutrition support
• Avoiding antidiarrheal medicines and, generally, antibiotics during E. coli O157 infection, because they may increase the risk of HUS. Avoid NSAIDs, which can harm the kidneys

Atypical HUS

Complement-blocking medicines, eculizumab or ravulizumab, have transformed treatment. They require meningococcal vaccination because they increase the risk of meningococcal infection.

Complications

• long-term kidney damage, protein in the urine and high blood pressure
• chronic kidney disease or kidney failure in a minority
• brain complications such as seizures or stroke
• diabetes from pancreatic damage, rarely
• death, uncommon in children with modern care (around 1 to 5 percent in typical HUS)

Outlook

Most children with typical HUS recover full kidney function within weeks. Some have lasting kidney effects, so follow-up for blood pressure, urine protein and kidney function is recommended for at least 5 years. Atypical HUS has a higher risk of relapse and kidney failure without complement-blocking treatment.

Prevention

• cook ground beef to 160 °F (71 °C), checked with a food thermometer
• avoid unpasteurized milk, juice and cheese
• wash produce thoroughly
• wash hands after using the toilet, changing diapers, touching animals and before preparing food
• avoid swallowing water in lakes, ponds and pools
• keep children with diarrhea out of childcare and pools until cleared

Frequently asked questions

What causes hemolytic uremic syndrome?

Most cases in children follow infection with Shiga toxin-producing E. coli, such as O157:H7, from undercooked beef, raw milk, contaminated produce or water. Atypical HUS is caused by overactivity of part of the immune system called complement, often due to genetic changes.

What are the warning signs of HUS?

Peeing less, pale skin, tiredness, irritability, unexplained bruising or tiny red spots, and swelling, typically 5 to 10 days after diarrhea begins. Any child with bloody diarrhea should be seen by a doctor and watched for these signs.

Is HUS contagious?

HUS itself is not contagious, but the E. coli infection that causes it is. It spreads through contaminated food and water and from person to person, especially among young children. Careful handwashing reduces spread.

Should antibiotics be given for E. coli diarrhea?

Generally not for E. coli O157 and other Shiga toxin-producing strains, because some antibiotics may increase toxin release and the risk of HUS. Antidiarrheal medicines should also be avoided. Doctors decide based on stool test results and the overall situation.

Can you recover fully from HUS?

Most children recover full kidney function, often within weeks, even if they needed dialysis. A minority have long-term kidney damage or high blood pressure, so regular follow-up is important for several years after the illness.