Environmental Engineering Reference
In-Depth Information
TABLE 3.2
Substance Dose to Cause Illness
Microorganism
Approximate Number of Organisms (Dose)
Required to Cause Disease
Campylobacter jejuni
a
10
2
or fewer
Coxiella burneti
b
10
7
Cryptosporidium
spp.
c
10
1
-10
2
oocysts
Dracunculus, Ascaris, Schistosoma
1 cyst, egg, or larva
Entamoeba histolytica
d
10 - 20 cysts, one in a susceptible host
Escherichia coli
b
10
8
Giardia lamblia
c
-
f
5-10
2
cysts
Salmonella typhi
b,g
10
5
-10
6
Salmonella typhimurium
g
10
3
-10
4
Shigella
spp.
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
a
Robert V. Tauxe et al.,
“Campylobacter
Isolates in the United States, 1982 - 1986,”
MMWR CDC
Surveillance Summaries
, June 1988, p. 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 one 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).
an infectious dose. However, some viruses (and other microorganisms) do survive
and present a hazard to the exposed population. Not all viruses are pathogenic.
An indication of the difficulty involved in testing for the effect of chemicals is
given by Kennedy
8
“A typical chronic toxicology test on compound X, done
to meet a regulatory requirement with an adequate number of animals and an
appropriate test protocol, costs $250,000 to 300,000,” and requires two to three
or more years to complete. Information concerning the
acute
effect of ingestion
of toxic substances is available in toxicology texts.
9
RESERVOIR OR SOURCE OF DISEASE AGENTS
Humans as Reservoirs
Contamination of food and drink may occur either directly with human or domes-
tic animal feces or indirectly by contact with objects that have had contact
with infected waste. Infected persons may serve as reservoirs for many of these
diseases, and may shed infectious organisms in their feces. Urine is usually
