Common Germs, Contaminated Foods, and Risk Factors
Food poisoning occurs when contaminated food or beverages expose people to harmful microorganisms or toxins.
Contamination can happen on a farm, during food processing, in a restaurant kitchen, or at home.
Even foods that look fresh and smell normal may contain dangerous germs.
Understanding the most common causes of food poisoning can help you make safer food choices and prevent illness.
- Bacteria That Cause Food Poisoning
Bacteria are an important cause of foodborne illness.
Some multiply in food under unsafe conditions, while others can cause illness after a relatively small exposure.
Salmonella
Salmonella can be associated with raw or undercooked poultry, eggs, meat, and contaminated produce.
Symptoms can include diarrhea, abdominal cramps, and fever.
Campylobacter
Campylobacter is commonly associated with raw or undercooked poultry and cross-contamination from raw meat.
Infection can cause diarrhea, fever, and stomach cramps.
- coli
Certain strains of Escherichia coli can cause severe intestinal illness.
Potential sources include undercooked ground beef, contaminated produce, and unpasteurized products.
Some strains can lead to serious complications, including kidney problems.
Bloody diarrhea after a suspected foodborne illness warrants prompt medical attention.
Listeria
Listeria can contaminate certain ready-to-eat foods, deli products, and unpasteurized dairy products.
It is particularly concerning during pregnancy, when infection can cause severe complications for the pregnant person and fetus.
- Viruses That Spread Through Food
Norovirus is a major cause of foodborne illness.
It can spread when an infected person handles food without appropriate hygiene, when food or water is contaminated, or when people touch contaminated surfaces and then their mouths.
Norovirus commonly causes sudden vomiting, diarrhea, nausea, and abdominal cramps.
It can spread rapidly in households, schools, healthcare facilities, and other shared environments.
- Parasites and Contaminated Water
Some foodborne parasites spread through contaminated water, raw or undercooked foods, or produce exposed to contaminated environments.
Depending on the parasite, symptoms may include prolonged diarrhea, abdominal discomfort, bloating, and weight loss.
Diagnosis and treatment differ from those for common bacterial or viral infections.
Use safe drinking water, wash produce under running water, and follow appropriate cooking recommendations to reduce risk.
- Foods Commonly Linked to Food Poisoning
Some foods are more likely to carry harmful germs when they are raw, undercooked, unpasteurized, or handled improperly.
Examples include:
- Raw or undercooked poultry and meat
- Raw or undercooked eggs
- Raw seafood and shellfish
- Unpasteurized milk, juice, and certain cheeses
- Unwashed fruits and vegetables
- Raw sprouts
- Cut melon that has been improperly stored
- Raw dough or batter containing uncooked flour
- Refrigerated ready-to-eat foods handled or stored unsafely
Risk depends on how food is produced, handled, cooked, and stored—not simply on the type of food.
- Improper Cooking and Food Storage
Cooking helps destroy many harmful microorganisms, but food must reach the appropriate internal temperature.
Leaving perishable food at room temperature also creates an opportunity for some bacteria to multiply.
The USDA identifies 40°F to 140°F as the temperature danger zone.
Refrigerate perishable food within two hours, or within one hour when the temperature exceeds 90°F. Keep refrigerators at 40°F or below and reheat leftovers to 165°F.
- Cross-Contamination in the Kitchen
Cross-contamination occurs when harmful germs transfer from one food, surface, or utensil to another.
For example, cutting raw chicken on a board and then using the same unwashed board to chop lettuce can transfer germs to food that will not be cooked.
Prevent cross-contamination by washing hands and surfaces, using separate cutting boards when practical, and keeping raw meat juices away from ready-to-eat foods.
Do not wash raw chicken in the sink because splashing water can spread germs around the kitchen.
- Who Is at Greater Risk?
Anyone can develop food poisoning, but some groups face a greater risk of serious illness.
These include:
- Children under five
- Adults aged 65 and older
- Pregnant people
- People with weakened immune systems
- Individuals with certain underlying medical conditions
People in these groups should take extra care with raw or undercooked foods and seek medical advice earlier if symptoms develop.
How to Reduce Your Risk
Follow the four core food safety principles:
Clean: Wash hands and food-contact surfaces.
Separate: Keep raw animal products apart from other foods.
Cook: Use a food thermometer to verify safe temperatures.
Chill: Refrigerate perishable food promptly and maintain a cold refrigerator.
Also check food recalls and discard recalled products according to official instructions.
Frequently Asked Questions
What is the most common cause of food poisoning?
There is no single cause for every case.
Common causes include norovirus and bacteria such as Salmonella and Campylobacter.
Their relative importance varies by setting and type of illness.
Can food poisoning come from homemade food?
Yes. Food prepared at home can become contaminated through improper cooking, inadequate refrigeration, contaminated hands, or cross-contamination.
Can expired food cause food poisoning?
Food may become unsafe when stored too long or at improper temperatures.
However, expiration or quality dates alone do not reliably determine whether food contains harmful germs.
Follow storage instructions and discard food when safety is uncertain.
Can you get food poisoning from vegetables?
Yes. Produce can become contaminated during growing, harvesting, processing, transport, or preparation.
Rinse fresh produce under running water and avoid cross-contamination.
Conclusion
Food poisoning can originate from bacteria, viruses, parasites, or toxins introduced at many stages of the food supply.
Safe cooking, careful storage, clean preparation, and appropriate food choices can greatly reduce the risk.
