当前位置：Why are the Elderly More Susceptible
to Contaminants in Drinking Water?
Aging is associated with physiological, functional, and
behavioral changes that can result in increased vulnerability
to biological and chemical contaminants in drinking water.
As a group, the elderly are at increased risk of infection and
disease from microbial contamination due to many factors,
such as reduced immunity, frailty from malnutrition, or
existing chronic illness. In addition, decreased liver and
kidney function associated with aging affects how the body
processes chemicals, and irregularities of the thirst mechanism
alter fluid balance (
1,2). Exposure patterns for theinstitutionalized elderly may also differ in important ways
from patterns in other populations. As a group, the elderly
can suffer more severe consequences from infections such
as
Salmonella and E. coli O157:H7, and are at greater riskof dying from waterborne infections (
3,4).The Elderly are Particularly
Susceptible to Microbial Contaminants
The functioning of various immune system cells declines
with age, and immunity can be compromised by chronic
diseases, malnutrition, and treatment with pharmaceuticals—
all common in the elderly (
5). Aging also leads to hypochlorhydria,thought to result from chronic atrophic gastritis,
degenerative systemic illness, or the use of potent medications
that inhibit acid secretion. The resulting increased stomach
pH inhibits the defense against enteric pathogens like
Salmonella
(6). Decreased intestinal motility associated withmedications, other coexistent gastrointestinal diseases, and
more frequent use of antibiotics (
7) and diuretics, may alsoput older patients at greater risk.
Diarrhea, often a trivial illness in younger adults, can be
catastrophic in the aged population, resulting in hospitalization
or death (
8). Fluid losses are normally mediated byurinary concentration and an increased thirst response. With
age, some of these mechanisms are less effective. The rapid
dehydration that can result from diarrhea in the elderly may
have severe consequences, including decreased blood flow
in vital organs, infarction, and arrhythmias (
8).Common microbial agents responsible for acute diarrhea
in the elderly include
Salmonella, Shigella, Campylobacterjejuni
, E. coli O157:H7, Giardia, and Norwalk virus (8),which can all be waterborne. The elderly may also be more
susceptible to the effects of cryptosporidiosis (
9,10).Long-term Residential Care as a Risk Factor
A 1991 study reviewed diarrheal causes of death between
1979 and 1987 (
11). The majority of these deaths occurredamong those older than 74 years whose risk factors were
being white, female, and residing in a long-term care facility.
Currently some 1.6 million elderly people live in nursing
homes; 72% of them are female (
12).For the period between 1987 and 1996, the incidence
rate of reported diarrheal outbreaks in Maryland nursing
homes ranged from 11 to 34% (
7). In the nursing homesetting, outbreaks of diarrhea occur commonly during the
winter months, and both the Norwalk viruses and rotavirus
have been implicated in these episodes (
13). Outbreaks ofenterohemorrhagic
E. coli O157:H7 have also occurred inlong-term care institutions (
14,15). In nursing homes, thecase fatality rates for certain waterborne pathogens, such as
rotavirus and
E. coli O157:H7, can be two orders ofmagnitude greater than that in the general population (3).
In one nursing home outbreak of
E. coli O157:H7, 35% ofthe infected patients died (
14).Physiological Changes
and Chemical Contaminants
Few studies have addressed risks from chemical exposures
to the elderly. We do not know whether the elderly are more
susceptible to effects of lower doses of environmental
chemicals than other populations. The physiologic changes
that accompany aging affect the processes of absorption,
distribution, metabolism, and excretion, although it is not
known how these changes affect sensitivity to chemical
exposures. Liver size and liver blood flow decline with age,
which may result in decreased metabolic capacity. There is
also an age-related decline in renal function. However, older
patients seem to be
more sensitive to the effects of somedrugs and
less sensitive to the effects of others, so drugmetabolism, and presumably that of chemical contaminants,
is variable compared with younger adults.
Health effects of some chemical contaminants may be a
result of years of cumulative exposure. For example, there is
epidemiological evidence that ingestion of lead-contaminated
tap water contributes to increased bone lead levels in the
elderly (
16). Whether this is associated with increased healthrisks is unknown. Some evidence suggests that many years
of ingesting uranium in drinking water affects kidney
function (
17), and that long-term arsenic consumption indrinking water is associated with vascular diseases, kidney
disease, and certain cancers in older populations (
18,19).What Can Health Care Providers Do
to Reduce the Threat of Waterborne
Contaminants to their Elderly Patients?
Be alert to the possibility of diarrhea. The elderly may be
reluctant to admit to having chronic diarrhea—especially if
they are also incontinent—because they find it embarrassing.
Consider the possibility that acute diarrhea may be a result
of a waterborne pathogen, especially in the institutionalized
elderly.
Advise elderly patients who use private wells to have their
water tested regularly for microbial and chemical
contaminants. Patients whose water may be at risk for
microbial contamination should consider home water
treatment units or bottled water.
Become involved in local efforts to prevent contamination
of drinking water sources. See PSR’s
Safe Drinking WaterAdvocacy Kit
for strategies on how to become involvedin these advocacy efforts.