Which of the following is a major contributing factor to foodborne illness outbreaks?

Contaminated ingredients are a major contributing factor to foodborne illness outbreaks because they can introduce harmful pathogens such as bacteria, viruses, or parasites into food products. These contaminants can occur at any stage of the food supply chain, from farm to table, and can include issues like improper handling, poor sanitation, or environmental contamination. When these contaminated ingredients are used in food preparation, they can lead to widespread illness among consumers. Addressing the safety and source of ingredients is critical in preventing foodborne illnesses, which is why this option is particularly significant in food safety management practices.

The other options, while they may contribute to food safety issues, do not directly cause illness in the same way as contaminated ingredients do.