U.S. Food & Drug Administration Center for Food Safety & Applied Nutrition Foodborne Pathogenic Microorganisms and Natural Toxins Handbook

Most chapters include a statement on infectious dose. These numbers should be viewed with caution for any of the following reasons:

• Often they were extrapolated from epidemiologic investigations.
• They were obtained by human feeding studies on healthy, young adult volunteers.
• They are best estimates based on a limited data base from outbreaks.
• They are worst case estimates.
• Because of the following variables they cannot be directly used to assess risk:

Variables of the Parasite or Microorganism

• Variability of gene expression of multiple pathogenic mechanism(s)
• Potential for damage or stress of the microorganism.
• Interaction of organism with food menstruum and environment
• pH susceptibility of organism
• Immunologic "uniqueness" of the organism
• Interactions with other organisms

Variables of the Host

• Age
• General health
• Pregnancy
• Medications--OTC or prescription
• Metabolic disorders
• Alcoholism, cirrhosis, hemochromatosis
• Malignancy
• Amount of food consumed
• Gastric acidity variation: antacids, natural variation, achlorhydria
• Genetic disturbances
• Nutritional status
• Immune competence
• Surgical history
• Occupation

December 1991

mow@cfsan.fda.gov