Five bacteria cause the vast majority of food poisoning cases in the United States: Salmonella, Campylobacter, Clostridium perfringens, Staphylococcus aureus, and Shiga toxin-producing E. coli (STEC). Together with norovirus (a virus, not a bacterium), these pathogens account for roughly 9.9 million domestically acquired foodborne illnesses every year. Each bacterium has its own typical food sources, onset timeline, and warning signs, so knowing which one you’re dealing with can help you understand what to expect and when the situation is serious.
Campylobacter: The Most Common Culprit
Campylobacter causes an estimated 1.87 million foodborne illnesses per year in the U.S., making it the single most common bacterial cause of food poisoning. It’s most often linked to undercooked poultry, unpasteurized milk, and contaminated water. Symptoms include diarrhea (often bloody), cramping, and fever, typically starting two to five days after exposure.
Most people recover within a week without treatment, but Campylobacter carries a rare and serious complication: Guillain-Barré syndrome (GBS), a condition where the immune system attacks the nerves, causing weakness or paralysis. About 1 in every 1,000 people with a Campylobacter infection develops GBS. That sounds small, but Campylobacter is so common that it’s one of the leading triggers for the syndrome in the country. Some studies have found that as many as 8 in every 20 people diagnosed with GBS had a recent Campylobacter infection.
Salmonella: The Biggest Killer
Salmonella is responsible for roughly 1.28 million illnesses, 12,500 hospitalizations, and 238 deaths per year, the highest death toll of any single foodborne pathogen tracked by the CDC. You’re most likely to pick it up from eggs, poultry, meat, and unpasteurized milk, though outbreaks have also been traced to leafy greens contaminated with animal manure.
Symptoms appear 6 to 72 hours after eating contaminated food, with most people feeling sick within 12 to 36 hours. The illness typically involves sudden fever, abdominal pain, diarrhea, nausea, and sometimes vomiting, lasting two to seven days. Most healthy adults recover on their own, but young children, older adults, and people with weakened immune systems face a higher risk of severe dehydration or bloodstream infection.
E. Coli (STEC): Small Numbers, Serious Complications
Shiga toxin-producing E. coli, often called STEC or by its most notorious strain O157:H7, causes about 357,000 illnesses a year. The classic sources are undercooked ground beef, raw milk, contaminated produce, and unpasteurized apple cider. Symptoms usually begin three to four days after exposure and include severe stomach cramps and diarrhea that often turns bloody.
What makes STEC especially dangerous is hemolytic uremic syndrome (HUS), a complication where toxins produced by the bacteria damage small blood vessels and destroy red blood cells, leading to kidney failure. About 8 in 10 children with HUS have an underlying STEC infection. Warning signs that someone with diarrhea may be developing HUS include urinating much less than usual, unusual paleness in the cheeks or lower eyelids, unexplained bruising, tiny red spots on the skin, blood in the urine, extreme fatigue, and decreased alertness. HUS requires emergency medical care.
Staphylococcus Aureus: The Fastest Onset
Staph food poisoning stands apart from most foodborne illnesses because it’s caused not by bacteria growing in your gut, but by a toxin the bacteria have already produced in the food before you eat it. That’s why symptoms hit fast, usually within 30 minutes to 8 hours. Nausea, vomiting, and stomach cramps are the hallmarks, and the illness is typically short-lived, resolving within a day or two.
The critical thing to understand is that cooking kills the Staph bacteria but does not destroy the toxin. Once the toxin has been produced in food left at room temperature too long, no amount of reheating will make it safe. Foods commonly involved include deli meats, cream-filled pastries, and anything handled by someone carrying the bacteria on their hands.
Clostridium Perfringens: The Cafeteria Germ
Clostridium perfringens causes about 889,000 illnesses per year and is sometimes called the “cafeteria germ” because outbreaks cluster in settings that prepare food in large batches: school cafeterias, nursing homes, catered events, and buffets. The problem starts when cooked food, especially meats, gravies, and stews, sits in the temperature danger zone between 40°F and 140°F (4°C to 60°C) for too long. The bacteria’s spores survive cooking and then multiply rapidly as food cools slowly, growing fastest around 109°F (43°C).
Symptoms are usually limited to watery diarrhea and abdominal cramps, starting 6 to 24 hours after eating. Vomiting and fever are uncommon. Most cases resolve within 24 hours, making it one of the milder forms of food poisoning, though it can be dangerous for elderly or immunocompromised individuals.
Listeria: Low Numbers, High Stakes
Listeria monocytogenes causes only about 1,250 illnesses per year, a tiny fraction compared to Salmonella or Campylobacter. But those 1,250 cases lead to roughly 1,070 hospitalizations and 172 deaths, giving Listeria one of the highest hospitalization and fatality rates of any foodborne pathogen. The bacteria thrive in refrigerated environments, which is unusual. Common sources include deli meats, soft cheeses, smoked seafood, and unpasteurized dairy.
Pregnant women face particular risk. Listeria can cross the placenta and harm the fetus even when the mother’s symptoms are mild. The CDC estimates that 1 in 4 pregnant women who develop listeriosis lose their pregnancy or their baby shortly after birth. About 1 in 25,000 pregnant women in the U.S. are infected each year. Older adults and people with compromised immune systems are also highly vulnerable.
Vibrio: The Raw Shellfish Risk
Vibrio vulnificus is less common than the bacteria listed above, but it’s among the deadliest. You get it primarily from eating raw or undercooked shellfish, especially oysters. A 2014 study found that Vibrio vulnificus is fatal in nearly 1 in 5 people infected in the U.S., and earlier research put the mortality rate above 50%. People with liver disease, diabetes, or weakened immune systems are at the greatest risk. Infections spike during warmer months when bacteria multiply faster in coastal waters.
How to Lower Your Risk
Most bacterial food poisoning comes down to two failures: food wasn’t cooked to a safe temperature, or it was left in the danger zone too long. A food thermometer is the most reliable tool you have. The USDA recommends cooking all poultry (whole birds, breasts, wings, ground) to 165°F (73.9°C), ground meats like beef and pork to 160°F (71.1°C), and fish and shellfish to 145°F (62.8°C).
Beyond temperature, basic habits make a measurable difference: refrigerate leftovers within two hours, thaw frozen food in the refrigerator rather than on the counter, wash hands before handling food, and keep raw meat separate from produce and ready-to-eat items. For Listeria specifically, avoid deli meats and soft cheeses during pregnancy unless they’ve been heated until steaming. For Vibrio, the simplest protection is to avoid raw oysters, particularly if you have liver disease or a compromised immune system.