Table 3: Host factors that increase the risk of foodborne and waterborne infection and/or the severity of the disease. Modified from [9].

Host factor	Reason for increased risk or severity
Primary immunodeficiency	Immune system inadequate to combat infection
Secondary immunodeficiency: resulting from leukemias, treatment with cytotoxic drugs during organ transplantation, for cancers or autoimmune disease, irradiation treatment, treatment with corticosteroids, infection with HIV.	Immune system inadequate to combat infection
Excessive iron in the blood	High levels of iron increase growth of certain pathogens
Cirrhosis and other liver disease, kidney function (alcoholism)	Iron overload, immune system dysfunction
Stress (e.g. as a result of surgery)	Changes in metabolism reduce resistance to infection
Diabetes	Poor glycaemic control is associated with impaired neutrophil functions
Pregnancy	Altered immunity
Age < 1 year	Gut microflora evolving, may allow survival of pathogens and colonization by spores of Clostridium botulinum. Lack of developed immune system.
Age < 5 years	Lack of developed immune system
Age > 60-65 years	Immune system deterioration, also affected by chronic ailments
Nutritional deficiency either through poor absorption of food or inadequate food supply	Immune system inadequate
Consumption of antacids, particularly proton pump inhibitors	Increase survival of pathogens in stomach
Consumption of large volumes of liquids including water	Dilution of acids in the stomach, rapid transit through stomach
Ingestion of fatty foods (e.g. chocolate, cheese, hamburger) containing pathogens	Fat protects pathogens from acid in stomach