Food poisoning is an illness caused by eating food or drinking beverages contaminated with harmful bacteria, viruses, or parasites. It affects roughly 48 million people in the United States every year, leading to 128,000 hospitalizations and 3,000 deaths. Most cases are mild and resolve on their own within a day or two, but certain infections can become serious, especially in vulnerable groups.
What Happens Inside Your Body
When you swallow contaminated food, the harmful organisms or the toxins they produce reach your intestinal lining. Some bacteria release toxins that trigger your intestines to flood with fluid, producing watery diarrhea even before the cells themselves are damaged. Others directly infect and destroy the cells lining your gut, causing inflammation, cramping, and sometimes bloody stool. Your body may also kill off its own infected cells as a defense mechanism, which contributes to the damage but helps contain the spread.
The result is the familiar combination of nausea, vomiting, diarrhea, and stomach cramps. Some people also develop fever and chills, particularly when the infection triggers a broader immune response beyond the gut.
Common Causes
The pathogens responsible for the most illnesses, hospitalizations, and deaths in the U.S. are Salmonella, Norovirus, Campylobacter, E. coli, Clostridium perfringens, and Listeria. Norovirus is the single biggest driver of foodborne illness outbreaks, while Salmonella causes the most hospitalizations. Other notable culprits include Staph bacteria (which produce toxins in food that’s been left out too long), Hepatitis A, Shigella, and Vibrio species found in raw shellfish.
Each organism tends to show up in specific foods. Salmonella is linked to poultry, eggs, and produce. E. coli outbreaks often trace back to undercooked ground beef or contaminated leafy greens. Listeria is associated with deli meats, soft cheeses, and ready-to-eat foods that aren’t reheated. Norovirus spreads easily through any food handled by an infected person.
How Quickly Symptoms Start
One of the trickiest things about food poisoning is that the meal you blame isn’t always the one that made you sick. Incubation periods vary widely depending on the pathogen involved:
- Staph toxin: as fast as 30 minutes to 6 hours, because the toxin is already formed in the food before you eat it
- Salmonella: 6 to 48 hours
- Norovirus: 12 to 48 hours
- E. coli (toxin-producing strains): 1 to 3 days
- E. coli O157: 1 to 8 days
- Listeria: 9 to 48 hours for gut symptoms, but 2 to 6 weeks for the more dangerous invasive form that enters the bloodstream
Toxin-based food poisoning (from Staph or Clostridium perfringens) tends to hit fast and hard but also clears quickly. Infections that require bacteria to multiply in your gut take longer to develop and can last longer.
Food Poisoning vs. Stomach Flu
Both cause diarrhea, nausea, and vomiting, so telling them apart can be difficult. The biggest clue is timing. Food poisoning typically hits within two to six hours of eating contaminated food, while the stomach flu (viral gastroenteritis) usually takes 24 to 48 hours to develop after exposure. Food poisoning also tends to resolve faster, often within a day, while the stomach flu commonly lingers for about two days or more.
Symptom patterns offer another hint. Fever and chills are more common with the stomach flu, since it triggers a stronger systemic immune response. Food poisoning is more likely to cause intense vomiting and diarrhea right away, sometimes with blood in the stool if the infection disrupts the intestinal lining rapidly. That said, overlap is common, and many cases are never formally diagnosed.
Who Faces the Greatest Risk
Anyone can get food poisoning, but four groups face significantly higher odds of severe illness because their immune systems are less equipped to fight off infections.
Children under 5 have immune systems that are still developing. They’re three times more likely to be hospitalized from a Salmonella infection than older children and adults. E. coli O157 is particularly dangerous for this age group: 1 in 7 children under 5 diagnosed with it develop kidney failure.
Adults 65 and older lose some of the immune function that once helped them clear harmful germs efficiently. Nearly half of older adults with lab-confirmed Salmonella, Campylobacter, Listeria, or E. coli infections end up hospitalized.
Pregnant women are 10 times more likely than the general population to get a Listeria infection, which can cause miscarriage, stillbirth, or serious illness in newborns.
People with weakened immune systems from conditions like diabetes, liver disease, kidney disease, HIV, or autoimmune disorders, or from treatments like chemotherapy, are at elevated risk. People on dialysis, for instance, are 50 times more likely to develop a Listeria infection.
How It’s Diagnosed
Most food poisoning cases are diagnosed based on symptoms alone and never require testing. If your illness is severe or prolonged, a doctor may order a stool test to identify the specific virus, bacterium, or parasite responsible. Blood tests can reveal signs of certain infections or complications like dehydration. In some cases, a doctor will check for blood in the stool, which points toward a bacterial or parasitic cause rather than a viral one.
Treatment and Recovery
Replacing lost fluids and electrolytes is the single most important thing you can do. Dehydration, not the infection itself, is what sends most people to the hospital. If vomiting makes it hard to keep liquids down, take small, frequent sips of water, diluted fruit juice, broth, or a sports drink. Saltine crackers can help replace electrolytes too.
For young children, older adults, and anyone with a weakened immune system, oral rehydration solutions like Pedialyte are a better choice than water or sports drinks because they contain a precise balance of glucose and electrolytes designed for faster absorption.
Over-the-counter anti-diarrheal medications can help with mild cases, but you should avoid them if you have a fever or bloody diarrhea. Those symptoms suggest a bacterial or parasitic infection, and slowing down diarrhea in that situation can actually keep the pathogen in your system longer.
Symptoms That Need Medical Attention
Most food poisoning passes without treatment, but certain signs indicate a case that’s moved beyond what your body can handle on its own. Seek medical care if you experience bloody diarrhea, diarrhea lasting more than three days, a fever above 102°F, or vomiting so frequent that you can’t keep any liquids down. Signs of dehydration also warrant a visit: urinating very little, a dry mouth and throat, or dizziness when you stand up.
Preventing Food Poisoning at Home
Bacteria multiply fastest between 40°F and 140°F, a range known as the “danger zone.” At the right temperature, bacteria can double in number in as little as 20 minutes. This is why leaving cooked food on the counter for extended periods is one of the most common causes of home food poisoning.
Cooking to the right internal temperature kills the pathogens that cause illness. Use a food thermometer rather than relying on color or texture. Whole cuts of beef, pork, and lamb need to reach 145°F (then rest for three minutes before cutting). Ground meat needs 160°F because bacteria get mixed throughout during grinding. All poultry needs 165°F. Leftovers should be reheated to 165°F as well.
Beyond temperature, the basics matter: wash your hands before and after handling raw meat, keep raw meat separated from ready-to-eat foods, refrigerate perishable items within two hours (one hour if it’s above 90°F outside), and wash produce under running water even if you plan to peel it.