The five most common causes of foodborne illness in the United States are norovirus, Campylobacter, Salmonella, Clostridium perfringens, and STEC (a type of E. coli). Together, these five pathogens account for the vast majority of the estimated 9.4 million foodborne illness episodes that occur each year. Norovirus alone is responsible for roughly 5.5 million of those cases, making it far and away the leading cause.
Each of these pathogens behaves differently: they show up in different foods, cause symptoms on different timelines, and vary dramatically in severity. Understanding which ones are most dangerous, and which foods carry the highest risk, can help you make smarter choices in the kitchen and at the table.
1. Norovirus: 5.5 Million Cases Per Year
Norovirus causes more foodborne illness than every other pathogen combined, accounting for about 58% of all food-related infections. It spreads through the fecal-oral route, meaning it gets into food when an infected person handles it without proper handwashing. It also spreads through contaminated water, direct contact with sick people, and even aerosols from vomiting.
The foods most often linked to norovirus are ready-to-eat items that aren’t cooked after preparation: salads, sandwiches, and fresh fruits. Raw shellfish, especially oysters, are a frequent source because the animals filter large volumes of water and concentrate viral particles in their tissue. Contaminated ice has caused outbreaks as well.
Symptoms typically hit 12 to 48 hours after exposure and include diarrhea, vomiting, nausea, stomach pain, and sometimes fever and body aches. Most people recover within a day or two, and while norovirus rarely causes death in otherwise healthy adults, it still ranks as the fourth leading cause of foodborne death overall due to the sheer number of people it infects each year.
2. Campylobacter: 1.9 Million Cases Per Year
Campylobacter thrives at the body temperature of birds, which makes poultry its primary vehicle. Most infections happen after someone eats raw or undercooked chicken, or eats another food that was cross-contaminated by raw poultry during preparation. The bacterium grows best between 99°F and 108°F, a range that closely matches the internal temperature of live chickens.
Symptoms usually appear 2 to 5 days after eating contaminated food and include diarrhea (often bloody), abdominal pain, fever, and nausea. In more severe cases, the infection can mimic appendicitis or inflammatory bowel disease. Most people recover completely within about a week without treatment, though Campylobacter is responsible for roughly 15% of all foodborne hospitalizations, making it the third leading cause of serious food-related illness.
3. Salmonella: 1.3 Million Cases Per Year
Salmonella is the single most dangerous common foodborne pathogen. While it ranks third in total number of infections, it causes more hospitalizations and more deaths than any other food-related germ. It’s responsible for about 35% of all foodborne hospitalizations and 28% of all foodborne deaths. Roughly 1 in 4 people hospitalized for foodborne illness have a Salmonella infection.
The foods most associated with Salmonella include raw or undercooked chicken and turkey, eggs, unpasteurized milk and juice, and raw fruits and vegetables. Contact with animals, particularly backyard poultry, reptiles, and small mammals, is another common route. Symptoms start anywhere from 6 hours to 6 days after exposure, a wide window that can make it hard to pinpoint which meal caused the problem. Expect watery diarrhea (sometimes bloody), fever, severe stomach cramps, and sometimes vomiting. Illness usually lasts 4 to 7 days.
4. Clostridium Perfringens: 889,000 Cases Per Year
C. perfringens is sometimes called the “buffet bug” because it thrives in food that’s been cooked in large batches and then left sitting at warm but not hot temperatures. Beef, poultry, and gravies are the most common sources. The bacterium produces spores that survive cooking, and when food cools slowly or sits on a steam table below 140°F, those spores germinate and multiply rapidly.
This is one of the milder foodborne illnesses. Symptoms appear 6 to 24 hours after eating and are limited to diarrhea and stomach cramps that typically resolve within 24 hours. Vomiting and fever are uncommon. Hospitalizations are rare, fewer than 500 per year, and deaths are extremely uncommon. The key to prevention is straightforward: serve cooked meat dishes hot within 2 hours of cooking, and keep hot food at 140°F or above.
5. STEC (Shiga Toxin-Producing E. Coli): 357,000 Cases Per Year
STEC, which includes the well-known strain E. coli O157:H7, rounds out the top five with an estimated 357,000 annual cases. While it causes far fewer infections than the other four, STEC punches above its weight in severity. The Shiga toxin the bacteria produce can damage the lining of blood vessels, and in a small percentage of cases, particularly in young children and older adults, infection leads to hemolytic uremic syndrome, a serious condition that can cause kidney failure.
Ground beef is the food most commonly associated with STEC, but outbreaks have also been traced to raw leafy greens, unpasteurized milk, and contaminated water. The bacterium lives in the intestines of cattle and can contaminate meat during processing. Cooking ground beef to an internal temperature of 160°F kills the organism reliably.
A Notable Runner-Up: Staphylococcus Aureus
Staph food poisoning doesn’t always make the official top five lists because the CDC’s most recent estimates focus on seven major tracked pathogens, but it’s common enough to deserve mention. Unlike the other pathogens on this list, Staph doesn’t make you sick by infecting your body. Instead, the bacteria produce a toxin in the food before you eat it, and it’s the toxin that causes illness.
This is why Staph food poisoning hits so fast. Symptoms, mainly nausea, violent vomiting, and stomach cramps, can start as soon as 30 minutes after eating. The foods most often involved are those handled after cooking and then left at room temperature: sliced deli meats, puddings, pastries, and sandwiches. Because Staph doesn’t compete well with other microbes in raw food, it’s almost always a problem with cooked or processed items that get recontaminated by human hands.
How Frequency and Severity Don’t Always Match
One of the most useful things to understand about foodborne illness is that the pathogens causing the most cases aren’t necessarily the ones causing the most harm. Norovirus infects millions but kills relatively few. Salmonella infects far fewer people but is the leading cause of hospitalization and death from foodborne pathogens. C. perfringens makes nearly 900,000 people sick each year, but almost all of them recover within a day without medical care.
The pathogens that kill the most people are a different list entirely. After Salmonella, the deadliest foodborne pathogens include Toxoplasma (a parasite found in undercooked meat and cat feces) and Listeria (found in deli meats, soft cheeses, and other ready-to-eat refrigerated foods). Listeria causes relatively few infections, but about 1 in 5 people who get sick from it die. Neither ranks in the top five by case count, but both are far more lethal per infection.
Practical Steps That Cover Most Risks
Because these five pathogens spread through different routes, no single precaution eliminates all risk. But a handful of habits cover most of the ground. Cook poultry to 165°F, ground meat to 160°F, and whole cuts of beef, pork, and lamb to 145°F with a 3-minute rest. Use a meat thermometer rather than guessing by color.
Refrigerate leftovers within 2 hours of cooking, and don’t let hot food cool slowly on the counter. This single step dramatically reduces C. perfringens risk. Wash your hands thoroughly before handling food that won’t be cooked again, like salads and sandwiches, since this is the primary way norovirus enters the food supply. Keep raw poultry separated from other foods during storage and preparation to prevent Campylobacter and Salmonella cross-contamination. And be cautious with raw oysters, unpasteurized dairy, and raw sprouts, all of which carry outsized risk relative to how often people eat them.