HUS stands for hemolytic uremic syndrome, a serious condition where toxins damage the small blood vessels, leading to kidney failure, destruction of red blood cells, and a dangerous drop in platelets (the cells that help your blood clot). It most commonly strikes children under 5 after a bout of food poisoning, though a rarer genetic form can appear at any age.
What Happens in the Body
HUS involves three problems occurring at once. First, red blood cells get shredded as they pass through damaged small blood vessels, causing anemia. Second, platelets get used up forming tiny clots inside those damaged vessels, which means easy bruising and bleeding. Third, the kidneys bear the brunt of this damage, often losing the ability to filter waste from the blood.
The damage doesn’t always stop at the kidneys. Neurological symptoms like seizures are common, and the heart, lungs, and pancreas can also be affected. About 20% of patients show signs of pancreatic injury. Neurological and cardiac complications are responsible for much of the serious harm HUS causes.
The Two Types of HUS
Typical HUS (Infection-Related)
The most common form is triggered by a bacterial infection, usually from a strain of E. coli called O157:H7. This bacterium produces Shiga toxin, a poison that invades the cells lining blood vessels, causes massive cell death, and triggers abnormal clotting inside the smallest blood vessels. O157:H7 alone is responsible for more than one million cases of diarrhea and roughly 2,000 cases of HUS worldwide each year. Other E. coli strains can also cause it. A 2011 outbreak in Germany involving a different strain (O104:H4) caused 3,816 infections, 845 cases of HUS, and 54 deaths.
The infection typically starts with painful, watery diarrhea and stomach cramps about four days after exposure. By day two or three of illness, the diarrhea often turns bloody. HUS itself develops about a week after diarrhea begins (median 6.5 to 7 days). At that point, the kidneys start failing, the child becomes pale and exhausted from anemia, and small red or purple spots may appear on the skin from low platelets.
Atypical HUS (Genetic)
Atypical HUS, or aHUS, is much rarer and has nothing to do with food poisoning. It’s caused by genetic mutations that leave part of the immune system, specifically the complement system, permanently overactive. The complement system normally helps fight infections, but when it can’t regulate itself properly, it attacks the body’s own blood vessel walls.
Several genes have been linked to aHUS, most involving proteins that are supposed to keep the complement system in check. When these proteins don’t work correctly, they fail to protect the surface of blood vessel cells, leaving them vulnerable to immune-mediated damage. Atypical HUS tends to begin more subtly, with fatigue, paleness, or unusual sleepiness, before progressing to kidney failure. It can also affect the heart and brain, causing complications like heart failure or seizures.
How HUS Is Treated
For the typical, infection-related form, treatment is primarily supportive. That means careful fluid management, monitoring kidney function, and dialysis if the kidneys stop filtering adequately. Blood transfusions may be needed for severe anemia. There’s no targeted drug for this form. The focus is on keeping the body stable while the damage from the toxin runs its course.
Atypical HUS is treated differently. Because the underlying problem is an overactive complement system, medications that block complement activation have become the standard of care. These drugs, first approved in 2011, work by shutting down the specific part of the immune cascade causing the damage. A newer, longer-acting version has since been developed. Some patients with aHUS initially receive plasma exchange, where their blood plasma is replaced with donor plasma to supply the missing or defective complement-regulating proteins. A significant number of aHUS patients need ongoing treatment to stay in remission.
Recovery and Long-Term Outlook
Most children with typical HUS survive. Mortality for infection-related HUS has dropped to about 1.3% based on data from recent decades, down from roughly 9.5% in earlier years. Atypical HUS carries a higher mortality rate, around 6.3%, and a much greater risk of lasting kidney damage.
Surviving HUS doesn’t always mean a full recovery, though. At one-year follow-up, about 28% of children with typical HUS still showed signs of kidney problems, such as reduced kidney function or the need for blood pressure medication. At five years, that number was closer to 44%. For atypical HUS, kidney outcomes are worse: all patients followed at one year in one study still had ongoing kidney issues, and 31% of non-infection-related HUS patients eventually needed a kidney transplant, compared to about 7% of those with the typical form.
How People Get Infected
The E. coli strains that cause typical HUS spread through contaminated food, water, or contact with infected animals or people. Undercooked ground beef is a classic source, but outbreaks have also been traced to raw milk, lettuce, sprouts, and contaminated water. Children are especially vulnerable because their immune systems and kidneys are still developing.
Cooking meat to safe internal temperatures kills the bacteria. Ground beef and sausage should reach 160°F (71°C), while steaks, roasts, and chops need at least 145°F (63°C) followed by a three-minute rest. Using a food thermometer is the only reliable way to confirm the temperature, since color alone isn’t a safe indicator. Thorough handwashing after handling raw meat, avoiding unpasteurized dairy, and washing produce carefully also reduce risk.
How HUS Differs From TTP
HUS is sometimes confused with a related condition called TTP (thrombotic thrombocytopenic purpura), because both involve small blood vessel damage, low platelets, and red blood cell destruction. The key difference is the underlying cause. TTP results from a deficiency in a specific enzyme that processes a blood-clotting protein. Testing for that enzyme’s activity level is currently the most reliable way to tell the two conditions apart. This distinction matters because the treatments are different: TTP requires urgent plasma exchange, while HUS treatment depends on which type is involved.