Symptoms vary depending on what is causing the illness. They may begin within a few hours or a few weeks depending on the cause.

Common symptoms are:

• Upset stomach.
• Vomiting.
• Diarrhea.
• Diarrhea with bloody stools.
• Stomach pain and cramps.
• Fever.
• Headache.

Less often food poisoning affects the nervous system and can cause severe disease. Symptoms may include:

• Blurred or double vision.
• Headache.
• Loss of movement in limbs.
• Problems with swallowing.
• Tingling or numbness of skin.
• Weakness.
• Changes in sound of the voice.

When to see a doctor

Infants and children

Vomiting and diarrhea can quickly cause low levels of body fluids, also called dehydration, in infants and children. This can cause serious illness in infants.

Call your child's health care provider if your child's symptoms include vomiting and diarrhea and any of the following:

• Unusual changes in behavior or thinking.
• Excessive thirst.
• Little or no urination.
• Weakness.
• Dizziness.
• Diarrhea that lasts more than a day.
• Vomiting often.
• Stools that have blood or pus.
• Stools that are black or tarry.
• Severe pain in the stomach or rectum.
• Any fever in children under 2 years of age.
• Fever of 102 degrees Fahrenheit (38.9 degrees Celsius) or higher in older children.
• History of other medical problems.

Adults

Adults should see a health care provider or get emergency care if the following occur:

• Nervous system symptoms, such as blurry vision, muscle weakness and tingling of skin.
• Changes in thinking or behavior.
• Fever of 103 degrees Fahrenheit (39.4 degrees Celsius).
• Vomiting often.
• Diarrhea that lasts more than three days.
• Symptoms of dehydration — excessive thirst, dry mouth, little or no urination, severe weakness, dizziness, or lightheadedness.

Many germs or harmful things, called contaminants, can cause foodborne illnesses. Food or drink that carries a contaminant is called "contaminated." Food can be contaminated with any of the following:

• Bacteria.
• Viruses.
• Parasites that can live in the intestines.
• Poisons, also called toxins.
• Bacteria that carry or make toxins.
• Molds that make toxins.

Understanding terms

The term "food poisoning" is commonly used to describe all foodborne illnesses. A health care provider might use these terms to be more specific:

• "Foodborne illnesses" means all illnesses from any contaminated food or beverage.
• "Food poisoning" means illness specifically from a toxin in food. Food poisoning is a type of foodborne illness.

How food becomes contaminated

Food can be contaminated at any point from the farm or fishery to the table. The problem can begin during growing, harvesting or catching, processing, storing, shipping, or preparing.

Food can be contaminated any place it's handled, including the home, because of:

• Poor handwashing. Feces that remains on the hands after using the toilet can contaminate food. Other contaminants can be transferred from hands during food preparation or food serving.
• Not disinfecting cooking or eating areas. Unwashed knives, cutting boards or other kitchen tools can spread contaminants.
• Improper storage. Food left out for too long at room temperature can become contaminated. Food stored in the refrigerator for too long can spoil. Also, food stored in a refrigerator or freezer that is too warm can spoil.

Common causes

The following table shows common causes of foodborne illnesses, the time from exposure to the beginning of symptoms and common sources of contamination.

Other sources

Bacteria that cause foodborne illnesses can also be found in swimming pools, lakes, ponds, rivers and seawater. Also, some bacteria, such as E. coli, may be spread by exposure to animals carrying the disease.

Anyone can get food poisoning. Some people are more likely to get sick or have more-serious disease or complications. These people include:

• Infants and children.
• Pregnant people.
• Older adults.
• People with weakened immune systems due to another disease or treatments.

In most healthy adults, complications are uncommon. They can include the following.

Dehydration

The most common complication is dehydration. This a severe loss of water and salts and minerals. Both vomiting and diarrhea can cause dehydration.

Most healthy adults can drink enough fluids to prevent dehydration. Children, older adults, and people with weakened immune systems or other illnesses may not be able to replace the fluids they've lost. They are more likely to become dehydrated.

People who become dehydrated may need to get fluids directly into the bloodstream at the hospital. Severe dehydration can cause organ damage, other severe disease and death if not treated.

Complications of systemic disease

Some contaminants can cause more widespread disease in the body, also called systemic disease or infection. This is more common in people who are older, have weakened immune systems or other medical conditions. Systemic infections from foodborne bacteria may cause:

• Blood clots in the kidneys. E. coli can result in blood clots that block the kidneys' filtering system. This condition, called hemolytic uremic syndrome, results in the sudden failure of the kidneys to filter waste from the blood. Less often, other bacteria or viruses may cause this condition.
• Bacteria in the bloodstream. Bacteria in the blood can cause disease in the blood itself or spread disease to other parts of the body.
• Meningitis. Meningitis is inflammation that may damage the membranes and fluid surrounding the brain and spinal cord.
• Sepsis. Sepsis is an overreaction of the immune system to systemic disease that damages the body's own tissues.

Pregnancy complications

Illness from the listeria bacteria during pregnancy can result in:

• Miscarriage or stillbirth.
• Sepsis in the newborn.
• Meningitis in the newborn.

Rare complications

Rare complications include conditions that may develop after food poisoning, including:

• Arthritis. Arthritis is swelling, tenderness or pain in joints.
• Irritable bowel syndrome. Irritable bowel syndrome is a lifelong condition of the intestines that causes pain, cramping and irregular bowel movements.
• Guillain-Barre syndrome. Guillain-Barre syndrome is an immune system attack on nerves that can result in tingling, numbness and loss of muscle control.
• Breathing difficulties. Rarely, botulism can damage nerves that control the muscles involved in breathing.

To prevent food poisoning at home:

• Handwashing. Wash your hands with soap and water for at least 20 seconds. Do this after using the toilet, before eating, and before and after handling food.
• Wash fruits and vegetables. Rinse fruits and vegetables under running water before eating, peeling or preparing.
• Wash kitchen utensils thoroughly. Wash cutting boards, knives and other utensils with soapy water after contact with raw meats or unwashed fruits and vegetables.
• Don't eat raw or undercooked meat or fish. Use a meat thermometer to make sure meat is cooked enough. Cook whole meats and fish to at least 145 F (63 C) and let rest for at least three minutes. Cook ground meat to at least 160 F (71 C). Cook whole and ground poultry to at least 165 F (74 C).
• Refrigerate or freeze leftovers. Put leftovers in covered containers in the refrigerator right after your meal. Leftovers can be kept for 3 to 4 days in the refrigerator. If you don't think you'll eat them within four days, freeze them right away.
• Cook leftovers safely. You can safely thaw frozen food three ways. You can microwave it. You can move it to the refrigerator to thaw overnight. Or you can put the frozen food in a leakproof container and put it in cold water on the counter. Reheat leftovers until the internal temperature reaches 165 degrees Fahrenheit (74 degrees Celsius).
• Throw it out when in doubt. If you aren't sure if a food has been prepared, served or stored safely, discard it. Even if it looks and smells fine, it may not be safe to eat.
• Throw out moldy food. Throw out any baked foods with mold. Throw out moldy soft fruits and vegetables, such as tomatoes, berries or peaches. And throw away any nuts or nut products with mold. You can trim away mold from firm foods with low moisture, such as carrots, bell peppers and hard cheeses. Cut away at least 1 inch (2.5 centimeters) around the moldy part of the food.
• Clean your refrigerator. Clean the inside of the refrigerator every few months. Make a cleaning solution of 1 tablespoon (15 milliliters) of baking soda and 1 quart (0.9 liters) of water. Clean visible mold in the refrigerator or on the door seals. Use a solution of 1 tablespoon (15 milliliters) of bleach in 1 quart (0.9 liters) of water.

Safety for at-risk people

Food poisoning is especially serious during pregnancies and for young children, older adults and people with weakened immune systems. These illnesses may be life-threatening. These individuals should avoid the following foods:

• Raw or undercooked meat, poultry, fish, and shellfish.
• Raw or undercooked eggs or foods that may contain them, such as cookie dough and homemade ice cream.
• Raw sprouts, such as alfalfa, bean, clover and radish sprouts.
• Unpasteurized juices and ciders.
• Unpasteurized milk and milk products.
• Soft cheeses, such as feta, brie and Camembert; blue-veined cheese; and unpasteurized cheese.
• Refrigerated pates and meat spreads.
• Uncooked hot dogs, luncheon meats and deli meats.

A diagnosis is based on a physical exam and a review of things that may be causing vomiting, diarrhea or other symptoms. Questions from your health care provider will cover:

• Your symptoms.
• Food or drinks you've had recently.
• Symptoms in people who ate with you.
• Recent changes in the drugs you take.
• Recent travel.

Your health care provider will examine you to rule out other causes of illness and check for signs of dehydration.

Your provider may order tests including:

• Stool sample tests to name the bacteria, viruses, parasites or toxins.
• Blood tests to name a cause of illness, rule out other conditions or identify complications.

When one person or a family gets food poisoning, it's hard to know what food was contaminated. The time from eating the contaminated food to the time of sickness can be hours or days. During that time, you may have had one or several more meals. This makes it difficult to say what food made you sick.

In a large outbreak, public health officials may be able to find the common food all of the people shared.

Treatment for food poisoning depends on how severe your symptoms are and what caused the illness. In most cases, drug treatment isn't necessary.

Treatment may include the following:

• Fluid replacement. Fluids and electrolytes, maintain the balance of fluids in your body. Electrolytes include minerals such as sodium, potassium and calcium. After vomiting or diarrhea, it's important to replace fluids to prevent dehydration. Severe dehydration may require going to the hospital. You may need fluids and electrolytes delivered directly into the bloodstream.
• Antibiotics. If the illness is caused by bacteria, you may be prescribed an antibiotic. Antibiotics are generally for people with severe disease or with a higher risk of complications.
• Antiparasitics. Drugs that target parasites, called antiparasitics, are usually prescribed for parasitic infections.
• Probiotics. Your care provider may recommend probiotics. These are treatments that replace healthy bacteria in the digestive system.

Drugs for diarrhea or upset stomach

Adults who have diarrhea that isn't bloody and who have no fever may take loperamide (Imodium A-D) to treat diarrhea. They also may take bismuth subsalicylate (Pepto-Bismol, Kaopectate, others) to treat an upset stomach. These nonprescription drugs are not recommended for children.

Ask your doctor about these options.

For most people, symptoms improve without treatment within 48 hours. To help keep yourself more comfortable and prevent dehydration while you recover, try the following:

• Let your stomach settle. Eat after your stomach is settled and you are hungry again.
• Replace fluids. Replace fluids with water, sports drinks, juice with added water or broths. Children or people at risk for serious illness should drink rehydration fluids (Pedialyte, Enfalyte, others). Talk to your doctor before giving rehydration fluids to infants.
• Ease back into eating. Gradually begin to eat bland, low-fat, easy-to-digest foods, such as soda crackers, toast, gelatin, bananas and rice. Stop eating if you feel sick to your stomach again.
• Avoid certain foods and substances until you're feeling better. These include dairy products, caffeine, alcohol, nicotine, and fatty or highly seasoned foods.
• Rest. Rest to recover from illness and dehydration.

You'll likely see your primary health care provider. In some cases, you may need to see a specialist in infectious diseases.

Be prepared to answer the following questions.

• When did your symptoms begin?
• Have the symptoms been continuous, or do they come and go?
• Have you had bloody diarrhea or stools?
• Have you had black or tarry stools?
• Have you had a fever?
• What have you recently eaten?
• Did anyone who ate the same food have symptoms?
• Have you recently traveled? Where?
• What drugs, dietary supplements or herbal remedies do you take?
• Had you taken antibiotics in the days or weeks before your symptoms started?
• Have you recently changed medications?