Viruses: These types of foodborne illnesses can be directly attributed to those who are already infected. If proper hygiene is not used by employees preparing food, viruses can be spread through the food. “Employees must wash hands” signs in restaurant bathrooms are present to remind employees that waste residue can give customers foodborne illnesses. Contaminated water used during the preparation process is also another common cause of such illnesses.

Parasites: Parasites can get attached to food through inadequate hygiene practices, just as viruses can. Both human and animal waste residue can cause these parasites to spread through water used in the food preparation process.

Chemicals: There are several sources of chemical poisoning that can occur. Unwashed fruits and vegetables often have high traces of pesticides that can be ingested. Toxins found in fish can cause illnesses for those who enjoy eating fish. Fish that feed on algae that produce toxins can create toxic chemicals that are then consumed. Fish not properly refrigerated can also produce toxins.