The most common symptoms of an E. coli infection are watery diarrhea, stomach cramps, nausea, and vomiting. Most people start feeling sick 3 to 4 days after exposure, though symptoms can appear as early as one day or as late as a week after contact with the bacteria. The illness typically resolves within a week in otherwise healthy adults, but certain warning signs signal something more serious.
Early Symptoms
The first thing most people notice is diarrhea, which starts watery and may become bloody over the next day or two. Stomach cramps range from mild to severe and tend to come in waves. Nausea and vomiting are common in the early phase of infection. Some people develop a low-grade fever, though not everyone does.
These symptoms overlap with many other foodborne illnesses, which is why E. coli is confirmed through a stool sample. If your doctor suspects E. coli, the lab will culture the sample and test for the specific toxins the bacteria produce. Without that test, it’s hard to distinguish E. coli from other causes of food poisoning based on symptoms alone.
Bloody Diarrhea and What It Means
Not all E. coli strains cause the same illness. The strains that make the news, called Shiga toxin-producing E. coli (STEC), are the ones that can cause bloody diarrhea. This happens because the toxin damages the lining of the intestines. Diarrhea often starts out watery and turns bloody within a day or two. If you see blood in your stool, that’s a signal to contact your doctor rather than wait it out.
Bloody diarrhea doesn’t automatically mean you’ll develop complications, but it does put you in a higher-risk category that warrants medical attention.
How Long Symptoms Last
Symptoms typically begin 3 to 4 days after you’re exposed, though the window ranges from 1 day to over a week. The acute phase, with the worst cramps and diarrhea, usually lasts 5 to 7 days. Most healthy adults recover without treatment in about a week. Children, older adults, and people with weakened immune systems can take longer and face a higher risk of complications.
During the illness, dehydration is the most immediate concern. Signs of dehydration include producing very little or very dark urine, extreme thirst, a dry mouth, dizziness, and crying without tears in young children.
Hemolytic Uremic Syndrome (HUS)
The most serious complication of STEC infection is hemolytic uremic syndrome, a condition where the toxin damages red blood cells and the kidneys. About 2% of people with the most common dangerous strain (O157) develop HUS. Some less common strains carry higher risk: roughly 8% of people infected with the O26 strain progress to HUS.
HUS typically develops about a week after diarrhea begins, often just as the diarrhea seems to be improving. The warning signs are distinct from ordinary stomach flu:
- Decreased urination: peeing much less than normal or not at all
- Pallor: losing pink color in the cheeks and inside the lower eyelids
- Extreme fatigue or irritability: especially in children, who may seem unusually cranky or lethargic
- Unexplained bruising or tiny red spots on the skin
- Blood in urine
- Decreased alertness
HUS is a medical emergency. It can lead to kidney failure and requires hospital treatment. Children under 5 and older adults are at the highest risk.
Symptoms That Need Immediate Attention
Most E. coli infections are unpleasant but resolve on their own. Certain symptoms, however, signal that you need medical care rather than rest and fluids. The CDC recommends contacting a doctor if you experience diarrhea or vomiting lasting more than 2 days, blood in your stool or urine, a fever above 102°F, signs of dehydration, or any of the HUS warning signs listed above.
One important note: antibiotics are not recommended for STEC infections. Research suggests they may actually increase the risk of developing HUS. Treatment focuses on staying hydrated and monitoring for complications. If you’re sick and suspect E. coli, let your doctor know before taking any leftover antibiotics on your own.
How E. coli Symptoms Differ From Other Food Poisoning
Several features set E. coli apart from a typical bout of food poisoning. The diarrhea is more likely to turn bloody. The incubation period is longer than something like staph food poisoning, which hits within hours. And while most foodborne illnesses are self-limiting annoyances, STEC infections carry a real risk of kidney complications that other common culprits like salmonella or norovirus do not.
If you’re experiencing watery or bloody diarrhea with severe cramps and you recently ate undercooked beef, unpasteurized dairy, raw sprouts, or contaminated produce, E. coli is worth considering. The only way to confirm it is through a stool test, so if symptoms are severe or bloody, getting tested gives you and your doctor a clearer picture of what you’re dealing with.