Food Poisoning Causes and How It's Treated

Food poisoning, also known as foodborne illness, is caused by the contamination of food by disease-causing agents (pathogens) such as bacteria, viruses, parasites, and natural toxins from molds and certain foods. Depending on the pathogen, symptoms can develop within minutes to days and include abdominal pain, diarrhea, and vomiting.

Food contamination can occur anytime from farm or fishery to the table. Fluid replacement is the main form of treatment, although antibiotics and antidiarrheal drugs may be used in severe cases. Left untreated, food poisoning can lead to severe dehydration and other potentially severe complications.

Causes of Food Poisoning

In the United States, over 47 million cases of food poisoning are estimated to occur each year, resulting in over 100,000 hospitalizations and over 3,000 deaths.

Bacteria are the most common cause of food poisoning. Viruses account for around a third of food poisoning cases, while certain parasites, fungi, and natural toxins account for the rest.

Bacterial Causes

The most common bacterial causes of food poisoning include:

• Campylobacter jejuni (found in undercooked poultry, raw dairy, and contaminated produce)
• Clostridium perfringens (sometimes called the "cafeteria bacteria")
• Salmonella (often the result of contaminated eggs or poultry)
• Escherichia coli (E. coli) (often associated with undercooked ground beef or raw milk)

Other less common bacterial causes include bacteria like Listeria, Shigella, Streptococcus, Staphylococcus aureus, Vibrio, and Corynebacterium.

In addition to direct infection, food poisoning can occur when a bacteria in contaminated food dies and secretes poisons called enterotoxins. Enterotoxins account for roughly 240,000 cases in the United States every year. Most cases are associated with undercooked meat and caused by bacteria such as:

• Clostridium botulinum (the cause of a potentially fatal illness called botulism)
• Clostridium perfringens
• Bacillus cereus
• Staphylococcus aureus

Viral Causes

In the United States, there are four viruses that account for the lion's share of viral food poisoning cases:

• Norovirus (which accounts for more than half of all cases)
• Hepatitis A
• Enterovirus
• Rotavirus (the most common cause in children)

These pathogens are primarily passed through the fecal-oral route in which stool from an infected person contaminates food. Poor handwashing and contaminated surfaces or kitchen tools are the most common routes of transmission.

Parasitic Causes

Most parasites associated with food poisoning are zoonoses. These are parasites transmitted from infected animals or fish to humans.

Some of the more common causes include:

• Flatworms (platyhelminthes), including Taenia species that cause beef and pork tapeworms
• Roundworms (nematodes), including Trichenella spiralis that cause trichinosis
• Protozoa, such as Cryptosporidia that cause cryptosporidiosis, Giardia lamblia that cause giardiasis, and Toxoplasma gondii that cause toxoplasmosis

Fungal Causes

Mycotoxins are a type of poison secreted by fungi. The toxins are produced in foods like tree nuts, peanuts, grains, and fruit that become contaminated with certain molds. Mycotoxins can directly cause food poisoning and can be passed in meat from affected livestock.

The six mycotoxins known to cause illness in humans include:

• Aflatoxins (most commonly found in peanuts, tree nuts, maize, and corn)
• Trichothecenes (most commonly found in maize, wheat, corn, peanuts, and rice)
• Zearalenone (most commonly found in maize, barley, oats, wheat, rice, and sorghum)
• Fumonisins (most commonly found in corn)
• Ochratoxins (most commonly found in cereal and dried fruit)
• Patulin (most often found in fruits)
  

Natural Toxins

Poisonous mushrooms are among the most well-known foods to contain natural toxins. But, there are many produced by beans, fish, and shellfish that can also cause food poisoning.

Some of the most common include:

• Mushroom toxins, including Amanita species such as the poisonous Death Cap mushroom
• Shellfish toxins, including Alexandrium found in mussels, clams, oysters, and scallops
• Fish toxins, including Gambierdiscus toxicus found in certain reef fish
• Phytohaemagglutinin, a toxin found in uncooked kidney beans and cannellini beans which is deactivated by cooking

How Food Poisoning Occurs

The contamination of food can occur when it is grown, harvested, processed, packaged, stored, shipped, or prepared.

At home or in restaurants, the most common causes of food poisoning include:

• Poor handwashing: This can lead to fecal-oral transmission if hands are not washed after going to the toilet. This can contaminate food or the surfaces or tools used to prepare them.
• Cross-contamination: This is when a germ or contaminant is passed to cooking surfaces or kitchen utensils that are not properly washed or disinfected. Cooking utensils, cutting boards, and other tools that are not fully cleaned can transmit bacteria to food.
• Improper storage: Leaving prepared foods unrefrigerated or storing frozen foods at an improper temperature can promote bacterial growth. This includes leaving eggs, dairy, or foods containing mayonnaise (such as cole slaw or potato salad) out for too long at room temperature.
• Non-pasteurized foods: Raw milk is a common source of food poisoning. Other juices or dairy products that are non-pasteurized can do the same.

In parts of the world where public sanitation is poor, food poisoning can occur from fruits and vegetables that are not peeled, meats and eggs that are not completely cooked through, or foods that are washed with tap water. Raw foods like sashimi, oysters, carpaccio, and even salads are common causes of food poisoning.

Symptoms

Food poisoning often causes severe gastrointestinal symptoms that develop when the body tries to purge the body of the toxin. This can lead to symptoms like:

• Nausea
• Abdominal cramps
• Diarrhea, including watery or bloody stools
• Vomiting
• Fever
• Headache

Depending on the pathogen, symptoms of food poisoning can develop within minutes to days. For instance, Staphylococcus aureus and Bacillus cereus can cause symptoms within 30 minutes of eating contaminated food, while Salmonella and hepatitis A can take up to six and 50 days, respectively, for symptoms to appear.

Complications

The main complication of food poisoning is dehydration caused when body fluids are lost through vomiting and diarrhea. If excessive amounts of water are lost, you can develop symptoms like:

• Fatigue and weakness
• Headache
• Extreme thirst
• Dry mouth
• Sunken eyes and loose skin
• Very dark urine
• Decreased urination
• Rapid heart rate
• Irritability and listlessness

In rare cases, food poisoning can lead to kidney damage. If the bacterial infection spreads into the bloodstream, it can lead to a potentially life-threatening immune overreaction called sepsis that may result in septic shock and death.

During pregnancy, food poisoning has been known to cause miscarriage or stillbirth and even lead to sepsis in the newborn.

When to Seek Emergency Care

Left untreated, dehydration can lead to a dangerous drop in blood pressure, resulting in a medical emergency known as hypovolemic shock.

Call 911 if you or a loved one experiences signs of severe dehydration, such as:

• Rapid breathing
• Racing heart
• Difficulty staying awake
• Fainting
• Confusion or delirium
• Low body temperature and cold skin
• No tears or wet diapers on babies
• Seizures

You also need to seek emergency care if vomiting and diarrhea last for more than two days in adults and 24 hours in children. Infants who vomit for more than three hours should also be taken to the ER, as well as any children who have signs of dehydration.

Diagnosis

Food poisoning can usually be diagnosed based on your symptoms and the events leading up to your symptoms. This may be accompanied by tests to identify the potential pathogen or rule out other causes of your symptoms.

The diagnostic tests may include:

• Stool culture to check for the presence of viruses, bacteria, or parasites
• Urinalysis to check for signs of kidney damage or complications from dehydration
• Blood tests like a complete blood count (CBC) and comprehensive metabolic panel (CMP) to check for certain infections or signs of complications from dehydration
  

Treatment

The main form of treatment for food poisoning is fluid replacement, which can usually be done at home. The aim is to replace fluids lost to vomiting and diarrhea to avoid dehydration.

This can be done in several ways:

• For adults or older children: Drink ample amounts of water or an oral replacement therapy (ORT) such as Ceralyte or Oralyte. You can also make your own rehydrating solution by adding 6 teaspoons of sugar and 0.5 teaspoons of salt to 1 liter of water. 
• For babies and younger children: Increased breastfeeding and/or bottle feeding is recommended. Toddlers can be given a commercial ORT called Pedialyte.

Avoid sports drinks like Gatorade, which cannot correct electrolyte losses because of their high sugar content. They may even worsen your diarrhea, promoting fluid loss.

For the majority of cases of food poisoning, medications are not necessary. However, in severe cases, the following drugs may be useful in preventing dehydration or resolving an underlying infection faster:

• Antidiarrheal agents like Imodium (loperamide) or Pepto-Bismol (bismuth) to control diarrhea
• Antiemetic drugs such as Zofran (ondansetron) to suppress vomiting
• Oral antibiotics like Zithromax (azithromycin) for severe bacterial infections
• Antiparasitics like metronidazole and sulfonamides for known parasitic infections
  

Prevention

Avoiding contaminated foods is the key to preventing foodborne illnesses. There are several simple ways to do this:

• Wash your hands for 20 seconds with soap and water before, during, and after preparing food.
• Wash your knives, cutting boards, countertops, and other utensils with soap and hot water.
• Rinse fresh fruits, vegetables, and bagged greens.
• Keep raw meat, eggs, seafood, and poultry away from other foods.
• Use separate cooking utensils and plates for raw meat, poultry, and seafood.
• Avoid unpasteurized milk and juices.
• Use a food thermometer to ensure meat, poultry, fish, and shellfish are properly cooked.
• Throw out foods that are past their expiration date, even if they do not smell or look bad.

When traveling to foreign countries, check the Traveler's Health guide offered by the Centers for Disease Control and Prevention (CDC) to ascertain the risk of food- and water-borne illnesses.

In areas of high risk, do not drink tap water or use ice made from tap water. You would also need to avoid eating fruits and vegetables you can't cook or peel.

Summary

Food poisoning is caused when foods are contaminated with bacteria, viruses, parasites, and toxins from mold and certain mushrooms, seafood, or fish. Symptoms include nausea, vomiting, diarrhea, and dehydration.

Most cases of food poisoning can be diagnosed based on symptoms, although tests may be ordered in severe cases to pinpoint the cause. Rehydration is the main form of treatment, although severe cases may benefit from antidiarrheal, antiemetic, antibiotic, or antiparasitic drugs.