Environmental Engineering Reference
Substance Dose to Cause Illness
Approximate Number of Organisms (Dose)
Required to Cause Disease
Campylobacter jejuni a
Coxiella burneti b
10 1 -10 2
Dracunculus, Ascaris, Schistosoma
1 cyst, egg, or larva
Entamoeba histolytica d
10 - 20 cysts, one in a susceptible host
Escherichia coli b
Giardia lamblia c - f
Salmonella typhi b,g
10 5 -10 6
Salmonella typhimurium g
10 3 -10 4
Shigella b,g 10 1 -10 2
Staphylococcus aureus b 10 6 -10 7 viable enterotoxin-producing cells per
gram of food or milliliter of milk
Vibrio cholerae b,g 10 6 -10 9
Virus, pathogenic 1 plaque-forming unit (PFU) or more
a Robert V. Tauxe et al., “Campylobacter Isolates in the United States, 1982 - 1986,” MMWR CDC
Surveillance Summaries (June 1988): 9.
b H. L. Dupont and R. B. Hornick, “Infectious Disease from Food,” in Environmental Problems in
Medicine , W. C. McKee (Ed.), Charles C. Thomas, Springfield, IL, 1974.
c R. M. Clark et al., “Analysis of Inactivation of Giardia lamblia by Chlorine,” J. Environ. Eng .
(February 1989): 80 - 90.
d Guidelines for Drinking Water Quality , Vol. 2, World Health Organization, Geneva, 1984, p. 44.
e Up to 10 cysts from beaver to human and 1 to 10 cysts to cause human to human infection.
f R. C. Rendtorff, “Experimental Transmission of Giardia lamblia,” Am. J. Hyg ., 59 , 209 (1954).
g Eugene J. Gangarosa, “The Epidemiologic Basis of Cholera Control,” Bull. Pan Am. Health Org .,
8 , 3 (1974).
contact (ingestion, inhalation, cutaneous) influence the inception of disease. The
experimental conditions pertinent to the determination of infectious dose levels
is important. The nature of the host subjects (human volunteers, monkeys, mice,
or other), health status of the host subjects, protocol for introducing the pathogen
dose to the subjects (oral, injection, aerosolization), and frequency of exposure of
the host subjects to the pathogen challenge are all important to the interpretation
of infectious dose values.
The low infectious dose for pathogenic viruses and protozoa would appear to
suggest that viral infections ought be readily spread through drinking water, food,
shellfish, and water-contact recreational activities. Fortunately, the tremendous
dilution that wastewater containing viruses usually receive on discharge to a
watercourse and the treatment given drinking water greatly reduce the probability
of an individual receiving an infectious dose. However, some viruses do survive
and present a hazard to the exposed population. Not all viruses are pathogenic
in the sense that their obligate destruction of host cells to sustain replication
and release of new virus particles may not trigger clinical symptoms of disesase
in the host. Nonetheless, heretofore unknown insidious relationships between