The most commonly cited example of a biological hazard for food handlers is Salmonella, a type of bacteria found in raw poultry, eggs, and meat that can spread to ready-to-eat foods through unwashed hands, shared cutting boards, or contaminated surfaces. But Salmonella is just one of many biological hazards. The term covers any living organism or substance produced by a living organism that can make someone sick through food, including bacteria, viruses, parasites, and molds.
What Counts as a Biological Hazard
A biological hazard in food safety is any microorganism or toxin from a microorganism that can cause illness or injury when consumed. These fall into four main groups: bacteria, viruses, parasites, and fungi (which includes yeasts and molds). What sets biological hazards apart from chemical or physical hazards is that they’re alive or were recently alive, and many of them can multiply in food if given the right conditions. Between 40°F and 140°F, bacteria can double in number in as little as 20 minutes. That temperature window is why food safety training calls it the “danger zone.”
Bacteria: The Most Common Category
Bacteria cause the majority of foodborne illness outbreaks linked to food handlers. Salmonella and Campylobacter are the most significant bacterial causes of foodborne illness across Europe and North America. Salmonella is especially tied to the handling of raw meat and ready-to-eat foods, where poor handling practices during processing and serving allow the bacteria to reach people’s plates.
Staphylococcus aureus is another bacterial hazard that food handlers introduce directly. This bacterium lives on human skin and in nasal passages, so it transfers easily when a food handler touches food without gloves or proper handwashing. It produces a toxin that causes vomiting and diarrhea within 2 to 4 hours of eating contaminated food. Unlike many other bacteria, the toxin itself isn’t destroyed by reheating.
Other important bacterial hazards include Listeria, which grows even under refrigeration and is particularly dangerous during pregnancy, and E. coli strains that produce a toxin capable of causing severe kidney damage. Salmonella typically causes diarrhea, fever, and abdominal cramps starting 6 to 48 hours after exposure.
Viruses Spread by Food Handlers
Norovirus is the single most common cause of foodborne gastrointestinal illness in many developed countries, causing millions of cases of diarrhea and vomiting worldwide each year. It spreads through food in two ways: food contaminated at its source (like shellfish or berries) and food contaminated by an infected handler during preparation or serving. For food handlers, the second route is the bigger concern.
What makes norovirus especially problematic is that infected workers can spread it even when they feel fine. Some people shed the virus without ever showing symptoms. Others return to work after their vomiting and diarrhea stop but continue shedding the virus for days or weeks. Once norovirus is on a food handler’s hands, it transfers easily to utensils, work surfaces, and food. CDC data from 2014 to 2022 shows that for viral outbreaks specifically, contamination from an infectious food worker through bare-hand contact was the leading contributing factor, responsible for 28% to 47% of cases depending on the time period analyzed.
Hepatitis A is the other major viral hazard from food handlers. It spreads through the fecal-oral route, meaning improper handwashing after using the restroom is the primary transmission mechanism. The FDA Food Code requires that food workers diagnosed with hepatitis A be excluded from the workplace, and those showing jaundice within the past 7 days cannot work around food.
Parasites and Fungi
Parasites are less common in commercial kitchens than bacteria or viruses but still pose real risks. Giardia spreads through contaminated water or food and causes prolonged digestive symptoms. Toxoplasma can be transmitted through undercooked meat. Anisakis, a worm whose larvae live in fish flesh, is the parasite most likely to cause allergic reactions in people who eat contaminated seafood, according to the European Food Safety Authority. Proper cooking and freezing protocols kill most parasites in food.
Molds and yeasts are the fungal side of biological hazards. While many molds are harmless, some produce toxins that accumulate in grains, nuts, and dried fruits. In a food service setting, mold growth on stored ingredients or improperly sealed foods is the most relevant concern.
How Food Handlers Spread Biological Hazards
CDC surveillance data from 2014 to 2022 found that contamination from an infectious food worker through bare-hand contact with food was the second most common contributing factor across all foodborne illness outbreaks, responsible for 16.5% of cases. Add in contamination through unknown hand contact or indirect contact, and the figure rises to nearly 30%. Ill food workers, whether touching food with bare hands or gloves, consistently rank among the top causes of outbreaks.
Cross-contamination is the other major pathway. When a food handler cuts raw chicken on a cutting board, then uses the same board or knife for salad greens, bacteria from the raw meat transfer directly to food that won’t be cooked again. The same thing happens when handlers touch raw meat packaging and then pick up bread, fruit, or other ready-to-eat items without washing their hands. Juices from raw meat or poultry that leak onto other foods in storage create the same risk.
One complicating factor: food handlers don’t always report being sick. Workers may avoid disclosing symptoms because they don’t want to lose shifts or leave their team short-staffed. Research on norovirus outbreaks has documented this pattern repeatedly, with workers continuing to prepare food while symptomatic or during the infectious tail end of their illness.
Foods Most Vulnerable to Biological Hazards
Certain foods support bacterial growth far more readily than others. These are classified as TCS foods, meaning they require time and temperature control for safety. The list includes raw and cooked meat, poultry, fish, eggs, dairy products, cooked rice and pasta, cut fruits and vegetables, and bean sprouts. Less obvious TCS foods include cream pies, custard-filled pastries, frostings made with butter or cream cheese, and even cold brew coffee.
Toppings can change a safe food into a risky one. Plain bread is shelf-stable, but adding generous amounts of spinach, tomato, cheese, or meat raises the moisture level enough for bacteria to grow if the food sits at room temperature. The key factor is moisture: bacteria need water to reproduce, so foods with higher water content require stricter temperature control.
Key Prevention Practices
The FDA Food Code requires food workers to wash their hands for at least 20 seconds using soap in a designated handwashing sink, with 10 to 15 seconds of vigorous rubbing that includes friction between fingers and attention to the area under fingernails. Handwashing is required after using the restroom, handling raw meat or poultry, touching the face, sneezing, and switching between raw and ready-to-eat food tasks.
Temperature control is equally critical. Keeping cold foods below 40°F and hot foods above 140°F eliminates the window where bacteria multiply fastest. Using separate cutting boards for raw meat and ready-to-eat foods, never reusing packaging from raw products, and sanitizing surfaces after contact with raw meat are all standard cross-contamination controls.
Exclusion policies exist for a reason. The FDA Food Code requires that any food worker experiencing vomiting or diarrhea be excluded from the establishment. Workers diagnosed with Salmonella, norovirus, E. coli, or hepatitis A face specific exclusion timelines, and those with a history of typhoid fever within the past three months cannot work around food. These rules exist because even gloved hands don’t fully prevent transmission. CDC data shows that gloved-hand contact from infectious workers was actually the most common contributing factor in viral outbreaks during the most recent reporting period, accounting for 42.6% of cases.