Download - 2. Vinculo Aguas Residuales-Tim O'Shea
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Wastewater and Health
Tim O’Shea MD, FRCPC, MPH
Associate Professor
Department of
Medicine
McMaster University,
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Outline
• Wastewater and Health – The Canadian
context
• Health effects
of
wastewater
– focus
on
infectious diseases
• Implications for
Peru
and
future
directions
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Wastewater and
Health
• In May 2000 the drinking water supply in
Walkerton Ontario
became
contaminated
with
E. coli
• The
local
water
supply
was
sourced
from
groundwater which was exposed to run‐off
from a cattle farm after particularly heavy rain
fall
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Walkerton Tragedy
• The result of this contamination was several
thousand acute
gastrointestinal
illnesses,
7
deaths and many individuals left with long
term illnesses
• Resulted in criminal charges against
individuals responsible
for
water
system
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Wastewater and
Health
• The use of wastewater for agricultural
irrigation has
several
potential
benefits:
– Release
of
higher
quality
sources
for
alternative
uses
– Increase water supply
– Provide nutrients
for
fertilization
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Wastewater and
Health
• The main risks associated with wastewater use
are related
to
public
health:
– Presence of bacterial, viral, protozol or heminthicpathogens
– Presence of
chemicals/pesticides
and
potential
for
health effects
• The risk
of
wastewater
use
is
exacerbated
when its use is unintentional or indirect
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Wastewater and
Health
• Indirect use occurs when treated, partially
treated or
untreated
wastewater
enters
the
agricultural irrigation system
• Health risks are similar with planned and
unplanned wastewater use but when
unintentional systems
to
mitigate
risk
are
usually not present
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Infectious Diseases
• Human feces contain ~ 1010 bacteria per gram,
the majority
of
which
are
non
‐pathogenic
• In the setting of infection with gastrointestinal
pathogens, stool
will
contain
large
quantities
of
the infecting organism
• Gastrointestinal illness
such
as
cholera,
typhoid
and E. coli O157:H7 can all be passed through exposure to contaminated water
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Infectious Diseases
• Viral pathogens can also be important causes
of water
borne
illness,
particularly
hepatitis
A
virus, adenoviruses, enteroviruses and
noroviruses
• Parasitic infections, especially helminthic
infections whose
life
cycle
includes
a soil
phase, are particularly important in
discussions of wastewater and health
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Wastewater and
Health
• Important to remember that health risks are
present both
for:
– Agricultural
workers
exposed
to
pathogens/toxins
in wastewater
– Those who
eventually
consume
potentially
contaminated foods
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Wastewater and
Health
• Overall risk to human health depends on:
– Excreted load
– Ability of organism to persist in environment
– Minimum infectious dose
– Ability of organism to enter latency
– Response of
human
host
(influenced
by
possible
immunity)
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Wastewater and
Health
• Given these factors most models rank relative
importance of
infectious
agents
as
follows:
1. Helminth infections
2. Protozoal and bacterial infections
3. Viral infections
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FIGURE 3. Prevalence of diarrhea in Peruvian children aged 0–35 months, 1995–1998.
William Checkley et al. Am. J. Epidemiol. 2003;157:166-175
©2003 by Oxford University Press
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Wastewater in
Peru
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Questions?