What is food poisoning?

Answer: Sickness that results from eating food contaminated with something bad.

Food poisoning (also known as food-borne illness) can be caused by many things including bacteria, viruses, parasites, molds, bacterial toxins, or toxic chemicals. The symptoms of the food poisoning depend on which particular organism or chemical was contaminating your food. Many types of food poisoning are contagious to other people.

Sometimes food is contaminated with bacteria, viruses, or parasites that can infect you and make you sick. The bacteria Salmonella1, E.coli2, and Campylobacter3 are common examples, as is the virus norovirus4. With this type of food poisoning, the food is not spoiled and it probably looks perfect. It did not sit out all night at room temperature. It is just a tiny bit contaminated with a nasty organism. Perhaps some E.coli O157:H1 got stuck to your spinach leaves or salmonella is residing in your peanuts. Your fresh berries may have a light dusting of norovirus. This type of food poisoning IS CONTAGIOUS! Cooking would destroy these organisms so food poisoning from them usually occurs via food that is eaten uncooked such as fresh produce or undercooked such as a pink hamburger. You won't get sick immediately upon eating foods contaminated with these organisms. They usually have incubation periods of at least 24 hours (rarely as short as 12 hours) to 8 days. Symptoms are typical of gastroenteritis and include vomiting and diarrhea. Occasionally, these illnesses can have deadly complications. When you are sick, you will have the bacteria/virus/parasite present in your feces and vomit and you will be contagious to other people. For more information about these illnesses and others please read my sections on bacterial and parasitic gastroenteritis and travelers diarrhea. For a list of EVERY organism that could make you sick from food, check out the FDA's "Bad Bug Book". This chart from the FDA includes lists of suspect foods.

Listeria5 is a type of food poisoning caused by the Listeria monocytogenes bacteria. It can cause fever, muscle aches and stiff neck in addition to diarrhea and vomiting. Listeria bacteria grow well in the refrigerator, and outbreaks of Listeria have been caused by deli meat, soft cheeses, hot dogs, cantaloupes, and ice cream. Listeria can be very serious and can cause stillbirth in pregnant women. Pregnant women should not eat lunch meat unless it has been reheated6. Cooking to 165 degrees F kills the Listeria bacteria and prevents illness. Listeria has a ridiculously long incubation period. It can take from 3 to 90 days to get sick! Most of the time it takes about 1 month from when you eat the contaminated food until you get sick. Here is an excellent article with tons of great information about Listeria.

Food Poisoning from bacterial toxins

This type of food poisoning occurs when food has been left out at room temperature or has cooled too slowly and bacteria have grown on it. A person is usually sick within 7 hours of eating the food and is not contagious to other people. Bacteria such as Staphylococcus aureus7, Clostridium perfringens8, and Bacillus cereus9 like to multiply on food that is sitting out at room temperature. So, if you leave the leftovers out for hours, these bacteria can set up camp. The Staphylococcus aureus bacteria are introduced to the food after it has been cooked--usually by a food handler. Clostridium perfringens and Bacillus cereus bacteria form heat stable spores that can withstand cooking and so could have been present in the food before it was cooked. These bacteria multiply on the food while it is cooling or if it is out of the fridge for a few hours. Staphylococcus aureus and Bacillus cereus produces toxins while they multiply on the food. It is the toxins that make you sick. Reheating the food will kill these bacteria but the toxins are very heat stable. They will still make you sick even if you boil the food. Symptoms of Staph food poisoning include nausea, vomiting, diarrhea, and abdominal cramps that begin 30 minutes to 7 hours after eating the contaminated food. It last less than 24 hours. Symptoms of Bacillus cereus food poisoning include nausea and vomiting that begins 30 minutes to 6 hours after eating. Bacillus cereus can produce a second illness caused by ingesting large numbers of the live bacteria (if you didn't reheat the food). They produce a different toxin in your stomach that makes you sick. In this case, you experience diarrhea and abdominal cramps that begin 6-15 hours after eating the contaminated food. Clostridium perfringens also loves to grow on food at room temperature. It produces its toxin in your stomach instead of on the food.(So, you would have been okay if you reheated the food to kill these bacteria.) Symptoms of Clostridium perfringens food poisoning include intense abdominal cramps and diarrhea 8-22 hours after ingestion. This illness usually lasts about 24 hours. All three of these types of bacteria can be present in the feces and vomit of the sick person. However, these illnesses are not considered to be contagious from person to person because of the large number of bacteria that it takes to make a person sick. However, a sick person who does not have clean hands, can easily contaminate some food and start the cycle over again.

Botulism10 is a type of food poisoning caused by a toxin produced by the bacteria Clostridium botulinum. It does not usually cause gastroenteritis symptoms but can be a very serious illnesses. Botulism causes a paralytic condition with symptoms of double vision, slurred speech, and muscle weakness. The Clostridium botulinum bacteria like to grow in low oxygen environments and food-borne outbreaks are usually caused by home-canned foods such as green beans. Boiling destroys the botulism toxin so please boil those canned goods prior to eating. Honey can contain botulism spores, so children less than 1 year old should never be fed honey.

Reheating your food (to 180°F) to kill infectious agents will keep you from getting sick from Salmonella, E.coli, Campylobacter, parasites, Botulism, Listeria, Clostridium perfringens, and norovirus. Reheating food will not protect you from food poisoning from Staphylococcus aureus or Bacillus cereus because their toxins are heat stable.

Food Poisoning from mold

There are many types of mold that can grow on food. Some are harmless or are supposed to be there (such as blue cheese) but others can make you sick. Some molds cause respiratory problems if the mold spores are inhaled. Other molds produce poisonous mycotoxins (such as cancer causing aflatoxin) that can cause serious illness. The general rule of thumb is to not eat any moldy food unless the mold is supposed to be there. For more information about moldy food go to the USDA website.

Aflatoxin poisoning--The fungi Aspergillus flavus and Aspergillus parasiticus produce toxic compounds called aflatoxins. These molds like to grow on corn and corn products, peanuts and peanut products, cottonseed, Brazil nuts, pecans, pistachio nuts, and walnuts. If a person or animal eats a lot of it, the aflatoxin will destroy their liver and they will die. If a person or animal just eats a tiny bit they probably won't get sick. However, the aflatoxins are carcinogenic and may contribute to liver cancer and other cancers. A cow that eats aflatoxin contaminated feed produce aflatoxin contaminated milk. So, humans can be getting small doses of aflatoxin from peanut butter, nuts, and milk. I wonder if the aflatoxin has any affect on the Salmonella in the peanut butter? Hmmmm. My family loves PB&J so Jiff had better be taking good care of those peanuts.

Food Poisoing from chemical toxins

Food poisoning from toxic chemicals is uncommon. Examples include eating food contaminated with high levels of pesticides, eating poisonous mushrooms, or eating Japanese puffer fish. Here is a little more detail.

Shellfish Poisoning--Shellfish such as mussels, clams, cockies, scallops, and oysters like to eat planktonic algae. The algae is full of toxins and so the shellfish can be full of toxins. Symptoms can be neurological or gastrointestinal depending on which type of toxins were present. Symptoms usually occur a few minutes to a few hours after consuming the toxic shellfish and can be fatal. Shellfish also like to accumulate norovirus, Hepatitis A and other unpleasant things they find in the ocean so I probably won't be eating shellfish. Never eat raw oysters. They often contain vibrio vulnificus which is a bacterium that can kill you.

Histamine Poisoning (scombroid poisoning)--Histidine is an amino acid present in protein. If certain bacteria are allowed to grow on food (if it is not stored properly) they can change histidine into histamine. Swiss cheese, tunas, mahi mahi, bluefish, sardines, mackerel, amberjack, and abalone have caused histamine poisoning. Symptoms begin minutes after eating the contaminated food. Symptoms include tingling or burning in the mouth, a rash on upper body, drop in blood pressure, headaches, itching of skin, nausea, vomiting, and diarrhea. Cooking, canning, or freezing does not reduce the toxic effect. Luckily, it is almost never fatal.

Pufferfish Poisoning (aka fugu poisoning)--Pufferfish contain a chemical called tetrodotoxin which can produce a rapid and violent death. The flesh of a pufferfish is usually not too toxic but other parts of the fish are. Other animals also contain tetrodotoxin including the California newt, parrotfish, Atelopus frogs, the blue-ringed octopus, starfish, angelfish, and xanthid crabs. It is best not to eat any of these animals. Could someone please tell me why "Fugu" is a delicacy in Japan? Surely, there is something else special to eat over there.

Mushroom Poisoning--There are many types of poisonous mushrooms that can kill you. There are no good ways to tell which wild mushrooms are poisonous and which are not. Cooking does not reduce the toxic effect. So, please don't run around tasting wild mushrooms. Please buy them at the grocery store. I'm going to stick with mushrooms on pizza and Campbells Cream of Mushroom soup. Make sure your toddler doesn't eat a mushroom growing in the yard.

Red kidney Bean poisoning--A toxic chemical called phytohaemagglutinin is found in many types of beans including white beans but is highest in red kidney beans. The beans need to be soaked in water for 5 hours and then boiled in clean water for 10 minutes. That decreases the amount of the toxic chemical. Symptoms of poisoning begin 1-3 hours after eating the undercooked beans and include nausea, vomiting, and diarrhea. The symptoms are severe but most people are better by the next day.

Honey poisoning--Honey can contain toxic chemicals depending on what type of plants the bees have had access to. Honey produced from the nectar of rhododendrons contains grayanotoxins. Shortly after the honey is ingested, the person may experience symptoms of dizziness, weakness, perspiration, nausea, vomiting, low blood pressure and shock. Luckily it is rarely fatal and lasts no more than 24 hours. Honey can also contain botulism spores so babies less than 1 year of age should never be fed honey. Don't let anyone eat a Rhododendron either.

Green Potatoes--Is it safe to eat those potatoes that have turned a little green? No. The green leaves, stems, sprouts, green eyes, and greenish skin contain a nerve toxin called solanine. It causes vomiting, diarrhea, and sometimes paralysis. Solanine can develop when potatoes are subjected to light. So, if your potatoes have greenish skin or have sprouted, throw them out. It takes a lot of the poison to hurt you, though. So, don't panic if you ate a green potato chip or a few bites of a slightly green potato.

There are many more scary organisms that you can acquire via contaminated food or water. Read the FDA's "Bad Bug Book" to further frighten yourself. This CDC website and the STOP Foodborne Illness website are also full of great information about food-borne illness. I haven't even begun to research what kind of worms people can catch from foods. I might be too frightened to even look into that.

--Annie Pryor, Ph.D.


I went to a restaurant on Lake Norman with my friend by boat and we met my husband there. He drove but he had been on a different boat earlier. They both ate blackened mahi. I went home with her on the boat and by the time we got back to her boat slip she had to go to her house and have diarrhea. I drove home. My husband was napping. This was Saturday afternoon. All evening he complained about being nauseous and dizzy. He kept blaming it on the boat. He didn't feel well enough to eat dinner. I think he had pretzels and soda water. After church the next day we went to lunch with the same friend. They were talking about how they both felt bad the night before. She also didn't feel like eating and had a bowl of cereal late night. So after all that I read the article and thought they both may have had scombrotoxin.


1. http://www.cdc.gov/salmonella/

2. http://www.cdc.gov/ecoli/index.html

3. http://www.cdc.gov/nczved/divisions/dfbmd/diseases/campylobacter/

4. http://www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus-factsheet.htm

5. http://www.fda.gov/Food/ScienceResearch/ResearchAreas/RiskAssessmentSafetyAssessment/ucm208993.htm

6.. http://www.who.int/ith/diseases/listeriosis/en/


8. http://www.foodsafety.gov/poisoning/causes/bacteriaviruses/cperfringens/index.html

9 http://www.foodsafety.gov/poisoning/causes/bacteriaviruses/bcereus/index.html

10. http://www.cdc.gov/nczved/divisions/dfbmd/diseases/botulism/

Food Poisoning from an infectious agent

Let me quickly mention the main difference between bacteria and viruses in case you don’t know. Viruses are not technically alive and do not replicate (reproduce) all by themselves. They attack your cells and your cells become like copy machines making many more viruses. If there is 1 virus in the potato salad and it sits in the sun all day, there will still be 1 virus in it at night. Alternatively, bacteria replicate all by themselves, and so there would be a huge increase in the number of bacteria in that potato salad.