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Foodborne Pathogens:
Causes of Food Poisoning & Foodborne Illness

Introduction to Foodborne Pathogens, Food Poisoning & Foodborne Disease

Preventing foodborne illness mainly involves maintaining proper hygiene and safe food handling practices.

Food poisoning, clinically known as foodborne illness, is a common public health problem caused by consumption of contaminated food.

The culprits responsible for causing this illness are microscopic organisms known as foodborne pathogens. Bacteria, viruses, and parasites can enter food if it is mishandled or infected.


Washing hands and surfaces often

Taking time to wash your hands frequently, thoroughly, and properly is the first-line defense against foodborne illness and other sicknesses.

You’ll get rid of germs, avoid becoming ill, and prevent spreading germs to others.


Cooking foods to safe temperatures

Just because your food looks done doesn’t mean it is done. The only way to know if your dishes are safely cooked is to use a food thermometer. The safe internal temperature for ground meat is 160°F; for fresh, raw, whole cuts of red meat it’s 145°F. Cook all poultry (incl. ground) to 165°F.


Refrigerating perishable foods

One of the most basic ways to make sure your food is safe is to set your refrigerator and freezer at safe temperatures for food storage: 40°F for your fridge and 0°F for your freezer. Bacteria capable of causing foodborne illness doesn’t grow or grows very slowly at these temperatures. 

Types of Foodborne Pathogens

The types of foodborne pathogens are varied with each having unique characteristics and effects. For instance, some foodborne pathogens are heat-resistant and survive cooking temperatures, while others thrive in cold storage. Similarly, their effects range from mild intestinal discomfort to severe dehydration, kidney failure, chronic arthritis, or even fatal conditions.


Bacteria are small, single-celled microbes that come in many shapes and are capable of reproducing themselves.



Viruses are much smaller than bacteria and cannot live outside a host, such as an animal or the human body.



There are about 20 different species of parasites that are known to cause illness in humans from contaminated food or water.


What is the Big 6 and why are they important?

Foodborne pathogens are invisible predators. They're microscopic and silent, and can cause lots of havoc when they contaminate our food and water. The "Big 6" pathogens are of particular concern because not only are they are highly infectious, but a small quantity can cause very severe illness.

You'll often see reference to the Big 6 in regard to retail food establishments and the public health community because training staff and addressing employee health and hygiene, to prevent the spread of foodborne disease, matters.

Find out more about the pathogens that make up the Big 6: Norovirus, Nontyphoidal Salmonella, E. coli, Shigella, Salmonella Typhi, , and Hepatitis A.

Foodborne Bacteria that cause illness

Bacillus cereus​

Commonly found in soil, Bacillus cereus can contaminate various types of food, particularly starchy foods like rice and pasta.
B. cereus produces toxins that lead to two types of illnesses: the diarrheal type (watery diarrhea), or the emetic type (nausea and vomiting). Symptoms usually appear within 6 to 24 hours.


Clostridium botulinum

Commonly associated with foods that are improperly canned, preserved, or stored, the illness caused by ingesting the potent neurotoxin produced by the pathogen Clostridium botulinum is called Botulism.
All forms of botulism can be fatal and are considered medical emergencies. Symptoms might include difficulty swallowing or breathing, muscle weakness, or blurry vision.


Cronobacter sakazakii

Found in dry foods like powdered milk, herbal teas, and starches, Cronobacter sakazakii can survive in dry environments, making it a significant concern for the powdered infant formula industry.
Cronobacter causes severe infections, especially in infants. Infection can lead to symptoms such as fever, irritability, poor feeding, and in severe cases, meningitis, or sepsis.



Campylobacter is found in raw or undercooked poultry, unpasteurized milk, and untreated surface water. Fewer than five hundred Campylobacter organisms can cause illness in humans. Even one drop of juice from raw chicken meat can infect a person.
Individuals exposed to these bacteria often experience watery bowel movements, nausea, and vomiting.


Clostridium perfringens

Common sources are beef, poultry, gravies, and foods cooked in large batches and held at unsafe temperatures. Places serving larger groups (hospitals, school cafeterias, prisons, catered events, etc.) where food is left for long periods at room temperature, are especially susceptible.
People with C. perfringens develop diarrhea and abdominal cramps within 6 to 24 hours.


E. coli (Escherichia coli)​

E. coli O157:H7 is a particularly harmful strain and can lead to severe gastric illness. The danger lies in undercooked ground beef, unpasteurized milk and juices, and contaminated fruits and vegetables.
Symptoms include bloody diarrhea, dehydration, and abdominal cramps 2-8 days after exposure. In the most severe cases, E. coli poisoning can cause kidney failure.


Hemolytic Uremic Syndrome (HUS)

HUS is characterized by the destruction of red blood cells, as well as the clogging of blood vessels in the kidneys, leading to kidney damage. Prompt medical attention is crucial for effective treatment and management.
People of all ages are susceptible to HUS, though it is most common in children younger than 5. About one in ten children who are infected with E. coli O157 develop HUS.


Listeria monocytogenes

Soft cheeses, cold cuts, and raw produce are some foods where these resilient bacteria thrive. Listeria causes high fever, severe headache, neck stiffness and nausea.
It can cause miscarriages and stillbirths, as well as serious and sometimes fatal infections in those with compromised immune systems, such as infants, older adults, and persons undergoing chemotherapy.



Salmonella is one of the most common foodborne bacteria worldwide. Typically found in the intestinal tract of animals, it is linked to any raw food of animal origin (meat, poultry, milk/dairy products, eggs, seafood), and some fruits and vegetables. A common contamination source is the unwashed hands of an infected food handler. Salmonella-contaminated food may not look or smell spoiled.



Shigella bacteria cause shigellosis, a gastrointestinal illness. Commonly found in feces, these bacteria often contaminate food and water sources through the poor hygiene practices of people working with food. Washing hands before handling food, and before eating is especially important. Cooking food thoroughly and washing fruits and vegetables can also prevent the transmission of Shigella.


Staphylococcus aureus and MRSA

Staphylococcus aureus (staph) is commonly found on skin, and in nasal passages, and respiratory tracts of humans. Staph can multiply at room temperature and produce toxins resistant to heat and most cooking methods. Foods left at room temperature for extended periods are common breeding sites for staph. A more virulent form of staph called MRSA, is resistant to many antibiotics.



Vibrio bacteria that thrive in warm seawater and can cause infections when individuals consume contaminated seafood or water. Vibrio infections can range from mild gastrointestinal symptoms to more severe illnesses such as cholera. Seafood must be safely cooked and stored at appropriate temperatures. Avoiding raw or undercooked seafood can reduce the risk of Vibrio infections.


Yersinia enterocolitica

Commonly found in raw or undercooked pork, as well as contaminated water and unpasteurized milk, Yersinia can cause fever and abdominal pain (may mimic appendicitis) and diarrhea. Symptoms typically develop 4 to 7 days after exposure and may last 1 to 3 weeks or longer.
Proper cooking and hygienic practices in food preparation can help prevent yersiniosis.


Foodborne Viruses that cause Illness


Often referred to as the stomach flu, Norovirus is notorious for its highly contagious nature and its tendency to cause outbreaks in settings such as restaurants, cruise ships, and nursing homes.
Symptoms typically occur one to two days after exposure, and include nausea, vomiting, abdominal cramps, diarrhea, fever, and muscle pain.


Hepatitis A

Hepatitis A is usually spread when the virus is taken in by mouth from contact with food, drinks, or objects contaminated by the feces of an infected person.
There are no special treatments for Hep A. Most people will feel sick for a few months before they begin to feel better. For some, Hepatitis A can result in a severe, potentially life-threatening liver infection.



A significant cause of foodborne illness among infants and young children, Rotavirus can lead to severe diarrhea, fever, and vomiting, leading to dehydration, and in severe cases, hospitalization.
There is no antiviral drug to treat rotavirus infection. Antibiotic drugs will not help because antibiotics fight against bacteria not viruses.


Hepatitis E

Hepatitis E Virus (HEV) is typically transmitted through the consumption of contaminated food or water. Sick animals, like pigs, can carry the virus and their meat or other products can get infected during processing. In addition, fruits, vegetables, and shellfish can also become contaminated if they come into contact with water contaminated with HEV.

Coming Soon

Other Viruses that can cause foodborne illness

Additionally, Sapovirus and Astrovirus are less famous than Norovirus and Hepatitis A. However, they also contribute to foodborne illnesses worldwide. In most cases, these viruses cause gastroenteritis, an inflammation of the stomach and intestines, leading to symptoms similar to those caused by the Norovirus.

Foodborne Parasites that cause illness


One common parasitic culprit is Toxoplasma Gondii, causing Toxoplasmosis - a disease that results in flu-like symptoms that can last for months. This parasite is often found in cat feces and uncooked or undercooked meat, especially pork, lamb, and venison.



Another notable parasite is Trichinella spiralis, which causes trichinosis. It is usually contracted by eating raw or undercooked meat of animals infected with the larvae of this worm, predominantly pork or wild game. Trichinosis infection can lead to severe symptoms like muscle pain, fever, and swelling of the face or eyes.



Cryptosporidium, causing Cryptosporidiosis characterized by watery diarrhea, is another parasite of concern. It's commonly associated with the consumption of water or food contaminated with infected feces.



Similarly, Giardia lamblia causes Giardiasis, characterized by diarrhea, excessive gas, stomach or abdominal cramps, and nausea. Giardiasis can be contracted from ill-prepared food, contaminated water, or through direct contact with an infected person.



Cyclospora cayetanensis is a parasite causing cyclosporiasis, an intestinal illness often acquired from consuming contaminated food, especially fresh produce. Symptoms include frequent bouts of watery diarrhea, fever, loss of appetite, nausea, and muscle aches. Untreated, the illness may last from a few days to a month or more. Symptoms seem to go away and then return one or more times (relapse).


Frequently Asked Question

The world of foodborne pathogens is vast and complex. These dangerous microscopic organisms can cause severe illness, discomfort, and in some extreme cases, death. Given their potential for harm, understanding them is crucial. More FAQ

Foodborne pathogens are bacteria, viruses, or other harmful microorganisms that cause diseases when you consume contaminated food or water. They constitute the primary cause of foodborne illnesses or food poisonings.

The action of foodborne pathogens differs. Some release toxins in food, triggering illness. Others invade the intestinal tract upon consumption. They multiply, trigger inflammation, and disrupt normal gut function, leading to symptoms such as vomiting and diarrhea.

Simple measures like washing hands thoroughly before handling food, ensuring food is properly cooked, avoiding cross-contamination of food, and promptly refrigerating leftovers minimize the risk of foodborne illnesses.

No, some individuals are more susceptible. Children, pregnant women, older adults, and people with weakened immune systems bear a higher risk of severe or life-threatening foodborne illnesses.

According to the Centers for Disease Control and Prevention, Norovirus and Salmonella are the most common foodborne pathogens. Norovirus causes the highest number of illnesses, whereas Salmonella tops the list for hospitalizations and deaths.

Yes. Some foodborne diseases can lead to long-term health effects like kidney problems (Hemolytic Uremic Syndrome from E. coli infection), chronic arthritis (Reactive arthritis from Salmonella), and brain and nerve problems (Neurologic symptoms from Campylobacter).

Doctors often diagnose foodborne illnesses based on symptoms and medical history. In some cases, stool testing can confirm the presence of a pathogen in your system.

If you suspect you might have a foodborne illness, seek medical attention immediately. Dehydration is a common result of foodborne illnesses, so drinking plenty of fluids is essential.

Foodborne Illness and Food Poisoning Resources

Food recalls play a crucial role in ensuring our safety against foodborne pathogens. They serve as the first line of defense by identifying and removing potentially contaminated food products from the market. When a potential health risk is detected, such as the presence of harmful bacteria or other contaminants, the food manufacturer or regulatory authorities initiate a recall to remove the affected products from circulation.
By promptly recalling contaminated food items, this preventive measure prevents further distribution and consumption, reducing the risk of widespread illness outbreaks. Food recalls are essential in protecting public health, as they alert consumers to potential dangers and allow them to avoid consuming the recalled products.
These recalls are not only important for our well-being but also for maintaining public trust in the food industry. They demonstrate that rigorous safety protocols are in place, and swift action is taken to address any potential hazards. Food manufacturers, retailers, and regulatory agencies collaborate to investigate the root cause of the contamination and implement preventive measures to avoid similar incidents in the future.
In addition to ensuring consumer safety, food recalls also serve as a crucial feedback mechanism for the food industry. Identifying the causes of contamination provides valuable insights into areas where improvements can be made in terms of production, handling, and packaging processes. This knowledge contributes to the continuous improvement of food safety standards across the board.

The Bad Bug Book is a valuable resource against foodborne illness. It provides essential information about different types of foodborne pathogens, such as bacteria, viruses, parasites, and toxins, that can cause illness when consumed. This book helps individuals, including consumers, food handlers, and healthcare professionals, to better understand the potential hazards associated with food and how to prevent foodborne illnesses.

The Bad Bug Book offers in-depth descriptions of various pathogens, their sources, symptoms they can cause, and the foods commonly associated with their contamination. It also provides guidance on proper food handling and preparation techniques to minimize the risk of foodborne illness. This resource is particularly useful for educating people about safe food practices and promoting a culture of food safety.

Additionally, the Bad Bug Book highlights important topics related to food safety, such as the principles of Hazard Analysis and Critical Control Points (HACCP) system, which is a preventive approach used in the food industry to identify and control potential hazards at critical stages of production.

The Food and Drug Administration (FDA) has developed this Employee Health and Personal Hygiene Handbook to encourage practices and behaviors that can help prevent food employees from spreading viruses and bacteria to food. It provides information in a question-and-answer format that food establishment management and food employees can use to prevent the spread of disease.

This handbook also provides easy reference to forms and tables that retail food establishments and the public health community may find useful when training staff and addressing employee health and hygiene matters

The Food Code is a model for safeguarding public health and ensuring food is unadulterated and honestly presented when offered to the consumer. It represents FDA’s best advice for a uniform system of provisions that address the safety and protection of food offered at retail and in food service.

This model is offered for adoption by local, state, and federal governmental jurisdictions for administration by the various departments, agencies, bureaus, divisions, and other units within each jurisdiction that have been delegated compliance responsibilities for food service, retail food stores, or food vending operations. Alternatives that offer an equivalent level of public health protection to ensure that food at retail and foodservice is safe are recognized in this model.

The 2017 Food Code (9th edition) reflects the agency’s continued commitment to maintaining cooperative programs with state, local, tribal, and territorial governments.

One of the most effective ways of preventing foodborne illnesses is access to reliable and authoritative resources. By gaining knowledge about these imperceptible culprits, we can protect ourselves and others from getting sick.

The Centers for Disease Control and Prevention (CDC) is one vital resource. You can find extensive information on different types of foodborne pathogens and the illnesses they cause. CDC’s surveillance systems diligently track reported cases of foodborne illnesses and provide annual summaries. They also offer expert advice on food safety, whether for your individual kitchen or for large-scale food service operations.

Another valuable resource is the World Health Organization (WHO), which provides comprehensive information about food safety from a global perspective. They also offer fact sheets on different pathogens, guides to handling and preparing food safely, and updates on global food safety incidents and trends.

The Food and Drug Administration (FDA) is another crucial tool in the fight against foodborne illnesses. Their website serves as an informative guide for consumers, providing advice on safe food handling, storage, and preparation.