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

Infective Dose Information

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

Because of the complexity of factors involved in making risk decisions, the multidisciplinary Health Hazard Evaluation Board judges each situation on all available facts.

December 1991

mow@cfsan.fda.gov

Hypertext last updated by mow/ear 1997-OCT-09