Food Poisoning: How Does Food Become Contaminated?

Food may become contaminated as it is produced, or as it isprepared.

Animals

Many foodborne microbes arepresent in healthy animals (usually in their intestines) raised for food. Meat and poultry can become contaminatedduring slaughter by contact with small amounts of intestinal contents.

Fresh fruits and vegetables can be contaminated if washed orirrigated with water contaminated by animal manure or human sewage.

Food Handling

During food processing, foodbornemicrobes can be introduced by infected humans handling the food or by crosscontamination with other raw agricultural products. For example, Shigella (bacterium) and Norwalk virus (Norovirus) can be introduced by an infected food handler'sunwashed hands.

Food Preparation

In the kitchen, microbes can be transferred from one food tothe other by using the same knife, cutting board, or other utensil withoutwashing in between. Fully cooked foodscan become re-contaminated if they touch other raw foods that containpathogens.

Food Storage

Many bacterial microbes need to multiply to larger numbersin food in order to cause disease. Underwarm and moist conditions, for instance, slightly contaminated food left outovernight can become highly infectious as bacterial microbes multiply. Prompt refrigeration or freezing preventsmost bacteria on food from multiplying.High salt, sugar, or acid levels also keep bacteria from growing.

Heating Food

Microbes are killed by heat.If food is heated to an internal temperature above 160F (78C), evenfor a few seconds, this is enough to kill most bacteria, viruses, orparasites. Toxins produced by bacteriavary in their sensitivity to heat. Forinstance, the toxin that causes botulism is inactivated by boiling, whereas thestaphylococcal toxin is not.