Food Poisoning Explained: Causes, Symptoms, And Treatments

We've all been there before: one minute you're chowing down on something delicious, and the next minute (well, usually several hours or days later) you're stuck on the toilet, clutching a trash can, and hoping someone will put you out of your misery. According to the Centers for Disease Control and Prevention (CDC), about 48 million Americans get some form of food poisoning each year. There are over 250 foodborne illnesses, most of which are caused by viruses, bacteria, or parasites. While extremely unpleasant, these conditions are usually quickly taken care of by our immune system. In some cases, however, food poisoning can be serious, even life-threatening. The CDC reports that approximately 128,000 people are hospitalized annually because of foodborne pathogens and about 3,000 die.

The CDC explained that any food can harbor disease-causing germs, but "raw foods of animal origin are the most likely to be contaminated, specifically raw or undercooked meat and poultry, raw or lightly cooked eggs, unpasteurized (raw) milk, and raw shellfish." Fruits and vegetables, especially when eaten uncooked, are also common avenues for food poisoning. Contamination can happen in the field, during processing, or in the kitchen. People can get sick because of cross-contamination, insufficient cooking, and improper storage of leftovers. Luckily, following a few basic food safety principles can greatly reduce your risk of getting sick.

Common symptoms of food poisoning

The symptoms of food poisoning vary somewhat based on which germ is causing the condition, but there are a few that almost always make an appearance. These include the "unholy trinity" of abdominal cramps, nausea/vomiting, and diarrhea. Abdominal cramping and pain can occur because of inflammation in your gastrointestinal tract caused by the virus or bacteria, as well as your body's own efforts to get the pathogen out as quickly as possible. These cramps can trigger nausea and vomiting. Many people experience an initial bout of very forceful vomiting as their body tries to get rid of the microscopic intruder. Diarrhea, defined as 3 or more loose or watery stools in a 24-hour period, is also common, thanks to abdominal cramps that speed up bowel movements. Inflammation prevents your intestines from effectively absorbing water as they normally would. Fever, chills, extreme fatigue, headaches, and muscle aches are also very common (via Healthline).

While these symptoms are guaranteed to make you miserable, they usually don't require professional intervention. You should, however, seek medical attention if you experience severe symptoms, such as bloody diarrhea, diarrhea that lasts more than 3 days, a high fever, and signs of dehydration, such as little or no urination, dry mouth, and dizziness (via the CDC).

What is the norovirus?

Although there are hundreds of germs that can cause food poisoning, a handful of them get the lion's share of attention because they're the most common or have the potential to cause serious disease outbreaks. Norovirus is by far the most common cause of food poisoning. According to the National Foundation for Infectious Diseases, there are 19–21 million cases of norovirus in the United States each year, including 56,000–71,000 hospitalizations and 570–800 deaths.

As the name implies, norovirus is a virus. Although often referred to as "stomach flu," it isn't related to influenza in any way. People get norovirus from contaminated food or water, touching contaminated surfaces, or close contact with sick individuals. Symptoms include the basics (cramping, diarrhea, and vomiting), along with a low-grade fever and muscle pain. Symptoms begin 12-48 hours after exposure and usually last 1–3 days. Individuals can continue to shed the virus in their stool for up to 2 weeks, meaning they can still infect others. Some lucky individuals experience no symptoms of norovirus infection but can still spread the disease (via the Mayo Clinic). Leafy greens, fresh fruit, and shellfish are the most common food sources of norovirus (via the CDC).

What is Campylobacter bacteria?

Campylobacteriosis is a type of food poisoning caused by Campylobacter bacteria. It causes an estimated 1.5 million illnesses in the United States each year, although many cases may go unreported. Cases are most common in summer, and many livestock animals carry Campylobacter in their intestines, liver, or other organs. Meat can become contaminated with bacteria during the slaughtering process. Campylobacter is more common than you might think; for instance, about 24% of raw chicken meat sold in grocery stores contains the bacteria. People become sick when they eat organs or meat from infected animals without thoroughly cooking them or as a result of cross-contamination when preparing food. Individuals can also get Campylobacter from unpasteurized milk from an infected animal or from fresh fruits and vegetables that have come in contact with contaminated soil or water. A very small amount of bacteria is needed to cause an infection.

Symptoms of campylobacteriosis begin 2-5 days after exposure and last about a week. The most common complaints are fever, stomach cramps, and diarrhea that is often bloody. Sometimes, people may also experience nausea and vomiting. Some individuals may shed the virus in their stool for weeks after they recover (via the CDC).

What is Salmonella?

Salmonella is a group of bacteria that can cause a type of food poisoning called salmonellosis. Although there are more than 2,500 types of Salmonella, fewer than 100 cause disease in people. Salmonella is found naturally in the intestines of humans and animals, and disease-causing strains can be picked up from consuming contaminated food or water or through close interaction with infected animals. Symptoms of salmonellosis include fever, diarrhea, and stomach cramps and can appear anywhere from 6 hours to 6 days after exposure. This type of food poisoning usually lasts 4-7 days, though some individuals may be sick for several weeks. The frequency and consistency of bowel movements may not return to normal for several months after the infection clears. 

Because of the heavy use of antibiotics in both humans and livestock, many strains of Salmonella are becoming resistant to these drugs, making it harder to effectively treat severe cases of salmonellosis. About 1.35 million Americans get salmonellosis each year. Of those, approximately 26,500 will be hospitalized and 420 will die (via the CDC). 

Raw or undercooked chicken, turkey, and eggs are the foods most likely to carry Salmonella. Improperly cooked beef, unpasteurized milk and juice, and uncooked fruits and vegetables may also carry the bacteria (via the CDC).

Food poisoning from Clostridium perfringens

Although it lacks the name recognition of baddies like norovirus and Salmonella, Clostridium perfringens (C. perfringens) is one of the most common causes of food poisoning. It causes nearly 1 million illnesses in the United States annually. C. perfringens is a bacteria that, when ingested, releases a toxin that causes GI upset. People can get C. perfringens from eating contaminated undercooked meat, as well as from eating properly cooked meat and meat-based gravies that have been kept at an unsafe temperature (between 40-140 degrees Fahrenheit) for too long. This is because C. perfringens makes spores. While thorough cooking kills the bacteria, the spores can survive the oven or stove. If allowed to sit in this dangerous temperature zone too long, they will grow into new bacteria.

That being said, it's not surprising that C. perfringens outbreaks often appear in situations where food is cooked in large batches and sits out for long periods of time. This includes meals served at school cafeterias, nursing homes, prisons, soup kitchens, and events with catered food. Many C. perfringens cases happen in November and December and have been linked to holiday gatherings. Symptoms appear 6-24 hours after exposure and usually last less than 24 hours. The bacteria's toxin causes stomach cramps and diarrhea, but vomiting and fever are rare (via the CDC).

Understanding Staphylococcus aureus

While most of us associate Staphylococcus aureus (staph) with nasty skin infections, the toxins these bacteria produce can also cause food poisoning. Meat can be contaminated with staph, or someone with staph on their hands can transfer it to food while handling it. When you consider the fact that about 25% of humans and livestock animals have staph on their skin or in their noses, it's easy to see why following food safety guidelines is so important. Although heat kills staph, it doesn't destroy the toxins that cause gastrointestinal illness. Foods that aren't cooked after handling, such as sandwiches and salads, pose the biggest threat. As is the case with most other types of foodborne illness, foods contaminated with staph don't necessarily smell or look bad.

Staph food poisoning tends to hit fast but resolves quickly. Symptoms can begin as soon as 30 minutes after eating contaminated food, though they may take up to 8 hours to appear. The good news is that the illness lasts no longer than a day. Individuals experience sudden nausea, vomiting, and stomach cramps, and most also have diarrhea. Severe illness is rare (via the CDC).

Exploring E. coli infections

Despite the bad rap they get, most types of Escherichia coli (E. coli) bacteria are harmless or even beneficial. Some, however, cause infections (such as urinary tract infections), while others produce a toxin that causes food poisoning. This last group of E. coli is known as Shiga toxin-producing E. coli (STEC). They are also sometimes referred to as verocytotoxic E. coli (VTEC) or enterohemorrhagic E. coli (EHEC). STEC cause approximately 265,000 infections in the United States each year, and about 36% of these are the result of one particular strain known as STEC 0157. Although widespread E. coli outbreaks garner a lot of press attention, only about 20% of E. coli food poisoning cases are part of a recognized outbreak.

STEC live in the intestines of ruminants like cattle. They shed the bacteria in their feces, and meat, milk, or other foods can become contaminated with this STEC-containing feces. Humans can get sick from eating undercooked meat, drinking unpasteurized milk or apple cider, eating soft cheeses made from raw milk, drinking contaminated water, or eating food handled by someone with a STEC infection who didn't wash their hands well after going to the bathroom. The incubation period for STEC is usually 3–4 days, although symptoms can appear anywhere from 1-10 days after exposure. STEC symptoms usually begin slowly and gradually build. Severe abdominal cramps, low-grade fever, diarrhea (usually bloody), and vomiting are common. Symptoms usually last 5–7 days (via the CDC).

Vibrio in saltwater and brackish water

Vibrio is a large group of bacteria that live in saltwater and brackish water. While there are many species, about a dozen can cause disease in humans, known as vibriosis. Cholera is a type of Vibrio bacteria, but it's classified separately from the species that cause vibriosis. 

The 3 strains that cause vibriosis in the United States are Vibrio parahaemolyticus, Vibrio vulnificus, and Vibrio alginolyticus. About 80% of Vibrio infections occur between May and October when ocean temperatures are warmer and the bacteria thrive. About 80,000 cases of vibriosis are reported each year, and approximately 45,000 of those are caused by Vibrio parahaemolyticus. Most people (about 52,000 of the 80,000 annual cases) get vibriosis from eating contaminated food — usually raw or undercooked shellfish, particularly oysters. The remainder is the result of getting contaminated water in a wound, which leads to a systemic infection rather than GI upset.

Most people recover from vibriosis within about 3 days, but 1 in 5 people with Vibrio vulnificus — the species that causes wound infections — will die of the condition, sometimes within just a day or two (via the CDC). Symptoms of gastrointestinal vibrio infection usually begin 2-48 hours after exposure and include watery diarrhea, nausea, stomach cramps, vomiting, fever, and chills (via the CDC).

The severity of Listeria

Listeriosis is a relatively uncommon but potentially very serious form of foodborne illness caused by the bacteria Listeria monocytogenes. There are about 1,600 cases of listeriosis in the United States each year, although many more likely go undocumented. This is because most individuals' bodies can clear the bacteria before they cause any harm. 

Pregnant women, newborns, those over 65, and people with weakened immune systems, however, can all experience symptomatic listeriosis. In these vulnerable groups, the bacteria spread from the GI tract to other parts of the body (known as invasive listeriosis), which requires hospitalization and can become life-threatening (via the CDC).

Symptoms of listeriosis appear 1-4 weeks after exposure. For pregnant women, the condition is usually relatively mild, with fever and flu-like symptoms, such as muscle aches and fatigue. However, the bacterial infection poses an extreme risk to her unborn baby. Older adults and those with a weakened immune system also have a fever and flu-like symptoms, but may also experience headaches, confusion, loss of balance, and convulsions. Common food sources for listeriosis include queso fresco and other soft cheeses, sprouts, melon, hot dogs, pâtés, deli meats, smoked seafood, and unpasteurized milk. Because of the extreme risk listeriosis can pose to her unborn child, pregnant women are cautioned to avoid many of these foods (via the CDC).

Botulism and canned food

Botulism has a well-deserved reputation as one of the most serious forms of foodborne illness, but luckily, it's quite rare. According to the CDC, there are about 110 cases of botulism in the United States each year, and only around 25% of these are foodborne botulism. The remainder of cases consist of infant botulism and wound botulism. While these conditions share many similar features of foodborne botulism, they're classified separately because of how the condition is acquired.

Botulism is caused by toxins produced by the bacteria Clostridium botulinum, as well as occasionally Clostridium butyricum and Clostridium baratii. Clostridium botulinum itself rarely makes people sick, but under the right conditions, these bacteria produce a toxin that can cause nerve damage, muscle paralysis, and death. These conditions include a low- or no-oxygen environment, low acid, low sugar, low salt, a specific amount of water, and a particular temperature range (via the CDC). The Mayo Clinic noted that home-canned low-acid foods such as fruits, vegetables, and fish are often the source of foodborne botulism. Symptoms typically begin 12-36 hours after ingesting the toxin and can progress rapidly. Common signs to look out for include dry mouth, difficulty swallowing and breathing, blurred vision, drooping eyelids, and facial weakness. Botulism is a medical emergency and can be fatal if left untreated. Paralysis of the muscles that control breathing is the most common cause of death.

Complications of food poisoning

For the majority of people, most types of foodborne illness are extremely unpleasant but short-lived and cause no lasting harm. Some people, however, are at greater risk of experiencing serious or even life-threatening complications. The immune systems of children under age 5 are still maturing and less able to tackle the germs that cause food poisoning. Young children become dehydrated more quickly than adults. Our immune systems become less effective as we age, so those over 65 are also at increased risk. Pregnant women and those with a compromised immune system are considered particularly vulnerable as well (via the CDC).

Foodborne pathogens can cause a variety of complications. For instance, while listeriosis may not have much of an effect on a pregnant woman, it can be devastating for her baby. Listeria infection during pregnancy causes death of the fetus in about 20% of cases and death of the baby shortly after birth in about 3% of cases (via the CDC). In about 5–10% of cases of E. coli infection, individuals develop hemolytic uremic syndrome (HUS), a potentially life-threatening condition in which the kidneys stop functioning properly (via the CDC). Campylobacter infections can cause a wide variety of complications, including long-term irritable bowel syndrome (IBS), temporary paralysis, and reactive arthritis. If the bacteria spreads to the bloodstream, it can cause life-threatening sepsis (via the CDC). Salmonella can also trigger reactive arthritis, which can last for months or years (via the CDC).

Treating food poisoning

Most healthy people's immune systems can clear most types of food poisoning on their own. It's essential to get plenty of rest and drink plenty of fluids and electrolytes to replace those lost from diarrhea and vomiting. Drinking ginger or mint tea may also help settle your stomach. 

If you're feeling brave enough to eat, it's best to stick to small, low-fat meals. Following the bland BRAT (bananas, rice, applesauce, and toast) diet is also commonly recommended. Adding probiotic supplements or probiotic foods, such as yogurt, to your diet may also help you feel better sooner. Some doctors believe it's acceptable to take OTC medications like bismuth subsalicylate (Pepto-Bismol) or loperamide (Imodium) to ease nausea, vomiting, and diarrhea, but other experts argue that it's best to not stand in the way of your body's attempts to get the pathogen out as quickly as possible (via WebMD).

If food poisoning requires hospitalization, it's usually because of moderate-to-severe dehydration. IV fluids and electrolytes can help rehydrate the body. Severe cases of food poisoning caused by bacteria may require antibiotics, but antibiotics won't have any effect on viral cases. Pregnant women with listeria are given IV antibiotics (via the Mayo Clinic). If caught early enough, an antitoxin can reduce the risk of complications from botulism. While the antitoxin can neutralize toxin that's still circulating in your blood, it can't reverse existing nerve damage, which is why early treatment is key. Antibiotics aren't recommended for foodborne botulism (via the Mayo Clinic).

Preventing food poisoning

It's impossible to have 100% protection from food poisoning. When you dine out, you don't have much control over how food is handled and prepared. You can, however, avoid ordering or eating the foods that are most likely to harbor disease-causing viruses and bacteria. This means eating all your meats, seafood, and eggs fully cooked and avoiding unpasteurized milk and juice. Pregnant women should steer clear of soft cheeses and other foods that are at high risk for Listeria (via the CDC).

When preparing food at home, the CDC recommends a common-sense 4-step food safety protocol. First, be sure to thoroughly wash your hands before handling food, as well as all utensils, cutting boards, and surfaces. Raw fruits and vegetables should also be rinsed. Second, avoid cross-contamination by keeping raw meat, seafood and eggs separate from other food when grocery shopping, in the fridge, and during preparation. Always use a separate cutting board, utensils, and plates for raw meat and eggs. Third, cook meat to the proper internal temperature to ensure any harmful bacteria are killed. For fish, most beef, lamb, and pork, the temperature to hit is 145 degrees Fahrenheit. For ground beef and pork, it's 160 degrees Fahrenheit. All poultry should be cooked to 165 degrees Fahrenheit. Finally, don't let food sit in the "danger zone" (40–140 degrees Fahrenheit), or long enough for bacteria to multiply. Refrigerate leftovers within 2 hours (or 1 hour if the ambient temperature is above 90 degrees Fahrenheit).

Understanding food recalls

Many cases of food poisoning are isolated incidents, but occasionally, more widespread outbreaks occur that can affect dozens or even hundreds of people. When these outbreaks are traced to a particular food or manufacturer, a recall is issued. Food recalls can help prevent outbreaks of foodborne illnesses before they happen. 

According to Food Safety News, food recalls are overseen by the Food and Drug Administration (FDA), a branch of the U.S. Department of Agriculture (USDA) known as the Food Safety and Inspection Service (FSIS). Food recalls linked to pathogens are considered a class I recall, meaning they represent "a health hazard situation in which there is a reasonable probability that eating the food will cause health problems or death." 

Other reasons for recalling a product include the presence of foreign objects, undeclared allergens, and undeclared sulfites. When it comes to foodborne illnesses, contamination is occasionally discovered by the manufacturer or regulatory agencies during testing or inspection. Other times, the situation isn't apparent until after people have become sick. Most food recalls related to foodborne illness center on E. coli, Salmonella, and Listeria.

If you discover you've bought food that's now the focus of a recall because of confirmed or suspected viral or bacterial contamination, throw it away immediately. It's also important to thoroughly wash any cookware, cutting boards, utensils, or plates that came in contact with the food. Wash and disinfect counters and refrigerator shelves where the food sat (via U.S. Department of Health & Human Services).