Most E. coli infections are not fatal, but a small percentage can be. In the United States, Shiga toxin-producing E. coli (STEC) causes roughly 265,000 illnesses and about 30 deaths each year. The danger comes not from the infection itself but from a serious complication called hemolytic uremic syndrome, or HUS, which develops in a minority of cases and can cause organ failure.
Which Strains Are Dangerous
E. coli is a large family of bacteria, and most strains live harmlessly in your gut. The ones that can kill are Shiga toxin-producing strains, particularly the well-known O157 type. These bacteria produce a toxin that damages the lining of your intestines and, in severe cases, attacks your kidneys and blood vessels. Of the roughly 97,000 O157 infections estimated in the U.S. each year, about 3,270 lead to hospitalization. Another 169,000 infections come from non-O157 strains, which generally cause milder illness and far fewer hospitalizations (around 400 per year).
Other types of E. coli cause urinary tract infections or traveler’s diarrhea, and while uncomfortable, these are almost never life-threatening in otherwise healthy people.
How a Routine Infection Turns Deadly
The path from a bad case of food poisoning to a life-threatening emergency follows a specific chain of events. Symptoms typically begin 3 to 4 days after exposure, though they can appear as early as one day or more than a week later. Most people experience watery diarrhea that turns bloody within a day or two, along with stomach cramps. For the majority, this resolves on its own within a week.
In roughly 5% to 20% of STEC cases, the Shiga toxin enters the bloodstream and targets cells in the kidneys. The toxin disrupts the protective lining of tiny blood vessels in the kidneys, triggering an immune response that destroys red blood cells and causes dangerous blood clotting in those vessels. The result is HUS: a combination of kidney failure, severe anemia, and dangerously low platelet counts. HUS typically develops about a week after diarrhea begins, often just as the gut symptoms seem to be improving.
Who Is Most at Risk
Children under 5 and adults over 65 face the highest risk of developing HUS after an E. coli infection. In children, French national surveillance data found a death rate of about 1% among those who developed HUS. Among adults who developed the syndrome, outcomes were considerably worse: a study of adult HUS patients in France found that nearly 20% died during hospitalization, over 60% needed dialysis, and more than half experienced serious neurological complications like seizures or strokes.
People with weakened immune systems, whether from medication, chronic illness, or other conditions, also face higher risk. Healthy adults in their 20s through 50s can develop HUS, but it’s less common.
Warning Signs That Need Emergency Care
The transition from a manageable illness to a dangerous one often happens quickly. The warning signs to watch for include:
- Decreased urination, which signals the kidneys are struggling
- Unusual fatigue or paleness, a sign of red blood cell destruction
- Small unexplained bruises or tiny red dots on the skin, caused by low platelet counts
- Swelling in the face, hands, or feet, from fluid retention as kidney function drops
These symptoms can develop 5 to 10 days after the initial diarrhea starts. If bloody diarrhea is followed by any of these signs, especially in a young child or elderly person, it requires immediate medical attention.
Why Antibiotics Make Things Worse
One counterintuitive fact about STEC infections: antibiotics can increase the risk of HUS rather than reduce it. When antibiotics kill the bacteria rapidly, they cause a sudden release of Shiga toxin from the dying cells, flooding the bloodstream with the very substance that causes kidney damage. For this reason, treatment for STEC infections focuses on supportive care, primarily fluids and close monitoring, rather than trying to eliminate the bacteria directly.
Long-Term Outlook After HUS
Surviving HUS doesn’t always mean a full recovery. Some patients, particularly those who needed dialysis during the acute phase, are left with permanent kidney damage that may require ongoing monitoring or eventually a transplant. The neurological complications that affect roughly half of adult HUS patients, including seizures and stroke-like episodes, can also leave lasting effects. Children generally recover more completely than adults, though some develop high blood pressure or reduced kidney function that only becomes apparent years later.
For the vast majority of people who get a STEC infection and recover without HUS, there are no lasting consequences. The infection clears, and the gut heals completely within a few weeks.