They need food, just as humans do, so they compete with us for our food supply. Food can supply nutrients that support the growth of microorganisms. The majority of cases of foodborne illnesses are not reported because the initial symptoms of most foodborne illnesses are not severe enough to require medical attention, the medical facility or state does not report such cases, or the illness is not recognized as foodborne. It is estimated, however, that millions of people become sick each year from contaminated food and several thousand die. Between 6.5 million and 81 million cases of foodborne illness and as many as 9,100 related deaths occur each year.
Bacterial pathogens are the most commonly identified cause of foodborne illnesses.
They are easily transmitted and can multiply rapidly in food, making them difficult to control. The CDC also are concerned about other bacterial pathogens, such as Vibrio vulnificus and Yersinia enterocolitica that can cause serious illnesses, and Clostridium perfringens and Staphylococcus aureus that cause less serious illnesses but are very common. Viral pathogens are often transmitted by infected food handlers or through contact with sewage. Hepatitis A and Norwalk viruses are proven to cause foodborne illnesses. Public health officials believe that the risk of foodborne illnesses is increasing.