Diabetes. What are the most common health complications associated with Type I or Type II diabetes? Diabetes diabetes complications …
Sensitive Subpopulations
Prepared By:
Jeffrey K Griffiths, MD MPHTM,
Director of the Graduate Programs in Public Health,
Tufts University School of Medicine, Boston MA
September 4, 2001
NATIONAL
RURAL WATER
ASSOCIATION
Executive Summary
The 1996 amendments to the Safe Drinking Water Act require the US
Environmental Protection Agency to consider susceptible subpopulations when
making health risk assessments These legal requirements are but one
manifestation of the general societal concern that exists around protecting
infants and children, the elderly, and people with impaired health or
unusual health risks In this white paper some issues of particular
relevance to the NRWA about drinking water sensitive subpopulations are
discussed
All people, no matter their personal beliefs or customs or health,
move in and out of being in a sensitive subpopulation through the normal
life cycle All of us begin life as infants, and hopefully end life having
lived to an advanced age Both of these life-cycle stages are composed of
sensitive individuals Pregnant women another sensitive subpopulation are
key to the survival
of our species Some people are in a sensitive
subpopulation for genetic reasons, and others acquire medical conditions
such as diabetes or AIDS that put them at special risk Many people do
not know that they are at increased risk of adverse health outcomes from
drinking water contaminants Furthermore, individuals in some sensitive
subpopulations are reluctant to identify themselves as different from the
general population Thus, practically speaking, public drinking water will
be made available to some people who are in sensitive subpopulation groups
These factors must be considered by the National Rural Water Association,
as it is a steward of the publics health
In addition to describing at least some of the sensitive
subpopulations, this white paper provides evidence for the growing number
of individuals who belong to one or more sensitive subpopulations As a
population we are living longer This is of course to be welcomed, though
it means that the percentage of the population that is elderly is growing
rapidly More and more individuals in the United States have chronic
medical conditions such as asthma and diabetes Some people with asthma
must take drugs steroids that
weaken their immune systems, and diabetics
are well known to be prone to infections Medical advances have made even
AIDS a chronic condition for some, and these individuals are again
especially sensitive to infections Others, lucky enough to receive a
transplantation, must take potent immunosuppressive drugs for the rest of
their lives, making them more likely to have malignancies and infections
Thus we as a population are changing, and many more of us find ourselves in
sensitive subpopulation groups
While there are differences between rural and urban water supplies, it
is difficult to argue that rural populations are devoid of sensitive
subpopulations Indeed, some noncommunity systems serve well-recognized
sensitive subpopulations, such as when an hospital, home for the elderly,
or school is involved Thus it must be concluded that the need to consider
sensitive subpopulations is one for all water suppliers in the United
States
It is inevitable that as science progresses, more groups of people
with specific sensitivities will be identified Between the population
shifts that suggest increasing population-wide sensitivity, and an
enlarging list of groups that will be
identified as being sensitive, the
issues regarding drinking water sensitive subpopulations are likely to
increase in importance and not decrease over time
A What is a sensitive subpopulation?
A1 Definitions
A2 Why the attention
B Who are sensitive subpopulations?
B1 Commonly-recognized groups
B2 Why the number of people in sensitive subpopulations is
increasing, and how
people move in-and-out of being in a sensitive subpopulation
throughout life
B3 Why are some people more sensitive than others? Some examples
B31 Cancers and Adverse Reproductive Risks
B32 Infections
B33 Genetic factors; pre-existing disease
B4 The number of sensitive subpopulation groups is likely to
expand
C Which sensitive Subpopulations are of concern to rural water systems?
D Is it possible to know who belongs to a sensitive subpopulation?
E Nontransient and Transient Noncommunity Systems
F Appendix of a few useful public health concepts relevant to sensitive
subpopulations
G References
A What is a Sensitive Sub-Population? Why the Attention?
A1 A sensitive sub-population is one that is at
increased risk of
some adverse health event or outcome after exposure to a contaminant in
drinking water By increased risk, this is defined as an increase when
compared to the total general population An adverse event or outcome is
generally a medical or health-related outcome This broad definition does
not pre-judge or restrict the reason or reasons for the sensitivity, but
does focus on the health effects of the sensitivity This focus is
appropriate because drinking water treatment and regulation is focused on
protecting the health of the population The Agency for Toxic Substances
Diseases Registry ATSDR, a division of the Centers for Diseases Control
uses a toxicological definition: A susceptible subgroup exhibits a response
that is different or enhanced when compared to the responses of most people
exposed to the same level of the contaminant The key concept is that the
sensitive subpopulation is affected when some other group - eg the rest
of the population, or the total population - is not, or is affected to an
lesser extent Indeed, in its December 2000 report to Congress EPA,
2000, the EPA used this definition: Sensitive subpopulations are defined
in this report as groups
of individuals who respond biologically at lower
levels of exposure to a contaminant in drinking water or who have more
serious health consequences than the general population This definition
also includes those individuals who have a greater level of exposure than
the general population as a consequence of biological factors that are
characteristic of the group to which they belong It can thus be seen that
the common elements of lower levels of exposure still lead to disease and
more serious consequences in the subpopulation are common definitional
threads[1]
A2 Why the attention? Altruism and legal requirements One can think
of at least two reasons First, anyone who is providing water to the public
would legitimately want to provide a safe and wholesome product The
knowledge that some groups of people might get sick from it would be
worrisome and provoke more interest in preventing any adverse effects
Secondly, the EPA is legally required by the 1996 reauthorization of the
Safe Drinking Water Act to consider the health effects of drinking water
contaminants and treatment on the total population and on sensitive
subpopulations, and to seek their input Several portions of the
1996 Safe
Drinking Water Act are quoted in the text box that follows on the next page
as examples Importantly, the setting of drinking water maximum
contaminant levels requires the consideration of sensitive populations
This regulatory and legal attention to subpopulations is grounded in
the long-standing recognition that some groups of people, such as infants
and children, pregnant and lactating women, and the elderly are more
susceptible to some illnesses The EPA has independently identified
children as a subpopulation that will receive additional focus, and it has
set up the Office of Childrens Health Protection to coordinate these
efforts described at the web site wwwepagov/children; EPA 1999 Many
AIDS groups lobbied for the language about subpopulations when the Safe
Drinking Water Act was reauthorized in 1996, because of the devastating
effect of Cryptosporidium infections on people with AIDS
B Who Are Sensitive Sub-populations?
B1 Commonly-understood groups Babies, young children, pregnant women,
and the elderly are the obvious examples of sensitive populations that are
within everyones common-sense experience Their ability to fight
off
infections is well-known to be lower than that of the general population
The frail elderly, those with some chronic illnesses or who have suffered
the effects of some prior illnesses, are particularly sensitive when
compared to the well elderly, who are otherwise hale and hearty
Similarly, people with AIDS or people receiving chemotherapy for cancers
are well-known to have reduced immunity People who have undergone a
transplantation eg of the kidney, liver, heart, or bone marrow are also
at increased risk of infections Some groups, such as pregnant women and
infants, are also more sensitive to the effects of nitrates, which causes
specific metabolic problems
B2 What is the traditional view of risk in the population, and is this
changing?
A traditional view of risk in the population is that risk is high
during the extremes of life, eg infancy and old age While true, this
view of susceptibility should be updated to reflect the realities of modern
life
People are living longer than they did The proportion of the
population that is elderly is rapidly expanding Indeed, the fastest
growing segment of the population is the population over 85 years of age
The graphs
below US Census Bureau, International Data Base provide
snapshots of the breakdowns of the US population in 1975 and in 2025 This
population pyramid shows that young children and adolescents were a far
larger part of the population than the elderly in 1975 This reflects
increasingly higher death rates as people age, starting in childhood
However, over time, the population will become on average older The next
graph shows the projected demographic makeup of the US in 2025 As can be
seen, most people will survive to age 70 in this projection This trend
is particularly true in many Central and Western states, and in rural
areas, which many young adults have migrated away from in search of work
Left Demographic Snapshot 1975 Classic triangular shape with many more
children than adults
Right Projected Demographic Profile of the US, 2025 House shape with
straight sides up to age 70 Everyone above the red lines are people who
will be alive in 2025, but who would not have been had they been born 50
years earlier
People are living longer with more chronic illnesses Public health
and medical advances have led to an increased lifespan in the US Lifespan
in 1900 was about 40 years of
age; it is currently 75 People are living
with chronic heart, lung, kidney, and liver diseases, and metabolic ones
such as diabetes Both asthma and diabetes are increasing at epidemic rates
in the US These chronic illnesses, along with many others, increase a
persons susceptibility to health insults This has led to the recognition
that the population includes the well elderly and the frail elderly,
with remarkably different sensitivities For example, people with tenuously
balanced heart failure may need to be hospitalized when they develop
gastroenteritis, while people with normal heart function would not
Thus, an updated view of susceptibility in the general population
should reflect these changes in the population In the graphs below, the
recognition of increased susceptibility to contaminants in infants and the
elderly in the traditional view left is updated to reflect our knowledge
about risks during pregnancy and during a frail old age
From this realization, an important central conclusion can be
reached
All people move in and out of being a part of a sensitive
subpopulation Everyone is an infant, and barring accidental death or bad
luck, everyone becomes
old; half of the population is female, and therefore
likely to undergo pregnancy Before our demise, many of us will be ill
with a number of chronic ailments, some of which may render us frail and
more susceptible to adverse health events Anyone who is not currently in a
sensitive subpopulation is at significant risk of joining one in the
future
B3 Why are some people more sensitive than the general population? The
answer to this question requires some explanation This explanation has
been grouped into three main areas
B31 People who suffer Cancer, or Adverse Reproductive Consequences
Cancers arise when the DNA of the cell the blueprint is damaged by a
chemical, which leads to a loss of control over cell multiplication Once
this control is lost, then the now malignant cell is free to continue
growing without hindrance Many scientists believe that several DNA
damaging events multiple hits may need to occur before an actual
malignancy will occur People who are exposed to high levels of carcinogens
in drinking water for a short period of time may develop cancer, as may
people exposed to low levels for prolonged periods People who have already
suffered a number of DNA
damaging events may be a sensitive subpopulation
For example, people who have already had one cancer and who can be
presumed to have had DNA damaging events are at much higher risk of
developing another cancer than people who have never had one Lastly, some
people may be born with the genetic disposition to cancer, as these may
run in families, and fewer external insults to a persons DNA may be
needed to lead to a malignancy Breast cancer is a common example
Pregnant women, infants, and children have cells that undergoing rapid
division and growth, and thus they are especially susceptible to agents
that can damage DNA Cells are most susceptible to suffering damage when
they are actively dividing and growing their DNA is physically more
exposed during this period For example, some water-borne contaminants
can affect reproductive integrity, eg cause sterility or decreased sperm
potency in men This occurs because the reproductive cells in this case,
the cells that form sperm are actively multiplying and producing a
continuous supply of sperm Similarly, some contaminants cause women to
miscarry, because the fetuss rapidly dividing cells are damaged, and the
remaining cells
either are nonviable or do not grow and divide properly a
lethal mutation The common thread that ties these forms of adverse
health effects together is that they result from damage to DNA, the
blueprint of the cell Sometimes this damage causes the cell to die, or it
causes the cell to grow without control Thus, the sensitive
subpopulations for this group of contaminants include people with many
growing and dividing cells pregnant women, infants, and children
Cancer is the second most common cause of death in the United States,
after cardiovascular diseases heart attacks, strokes, hypertension, etc
Ries, 2000; Howe 2001 The National Cancer Institute estimated in 1996
that approximately 82 million American alive today have an history of
cancer One of every four deaths in the US is from cancer, totaling 539,000
in 1996 About 12 million cases of non-skin cancer are diagnosed each
year, and about 13 million cases of skin cancer
Cancer mortality is distributed across the United States, and in many
states there is no particular rural versus urban pattern Historically,
cancer was clustered near large urban industrial centers, but this no
longer holds Note the scatter of red
high cancer counties distributed
through the Midwest and the Rocky Mountain states The graphs below show
total cancer death rates for white women by country during the period 1970-
1974 Death rates, not incidence rates, were chosen for this map since some
cancers, such as skin cancers, do not lead to significant illness,
subpopulation sensitivity, or death Atlas of Cancer Mortality, 1999
This map was created using the National Cancer Institutes On-Line Atlas,
which can be found at wwwncinihgov/atlasplus/
Context: Major issues
Many chemicals based on petroleum products are known to be
carcinogens The industrial production, use, and waste disposal
of these agents has led to contaminated ground waters throughout
the US
Pesticides, which can contaminate surface and ground waters, are
under increasing scrutiny
Certain heavy metals, such as arsenic, are carcinogens
The EPA has determined that between 1,000 and 10,000 cases of
bladder cancer arise each year as a consequence of chlorinating
water EPA, 1998 There is controversy around the possibility
that even
transiently high levels of disinfection byproducts
related to chlorination or bromination can or could lead to
spontaneous miscarriages Swan 1998; Waller 1998; EPA, 1998
Recently, lawsuits have been filed against water purveyors who
provided water with average trihalomethane levels within Federal
guidelines but whose seasonal levels were high
B32 Infections
Background:
One of the great public health advances of the past century was the
move to provide the population with clean potable water These measures led
to major decreases in the burden of infectious diseases in the US
population Okun, 1999 These measures predated antibiotics and most
vaccines; indeed, many people forget that the huge decrease in infectious
diseases in the US earlier this century was due to clean water, clean food,
and sewerage - not to modern medical advances The failure of drinking
water treatment, such as occurred in Walkerton, Canada, last year led to
many thousands of ill people and over a dozen deaths the exact numbers are
in dispute Thus even in advanced societies continuing water treatment is
absolutely crucial
The
thousands of infectious agents generally fall into 3 groups:
viruses, bacteria, and parasites, in order of increasing complexity Many
of these agents can be transmitted by contaminated drinking water Water
treatment kills, inactivates, or removes the vast majority of these
pathogens Parasites are generally more difficult to inactivate with
standard disinfection than either viruses or bacteria, and in fact some
eg Cryptosporidium cannot be killed with standard chlorination While
it is presumed that ground water systems are very unlikely to be
contaminated with infectious agents because of the filtering performed by
the ground, many recent outbreaks have occurred in ground water systems
because of wellhead contamination or distribution system flaws Ultraviolet
light appears to be effective against all three of these groups of
pathogens Sensitive populations can be unusually sensitive to any of
these agents Prions associated with mad cow disease and scrapie, a sheep
disease are believed to be a new or fourth class of infectious agents,
have never been shown to be transmitted in water, and are not currently of
any significant public health or scientific concern regarding water
Prions
will not be discussed again in this document given this information
Specifics:
Infants, because of their small size and naïve immune systems, are
well known to be especially sensitive to infectious diseases Being small
means they are easily overwhelmed, and being naïve means that their immune
systems do not know how to effectively fight off many infections Young
children are less sensitive than infants, but still more sensitive than
older children, adolescents, and adults Pregnant women are also relatively
immuno-compromised, and have been repeatedly shown to suffer more frequent
and more severe infections than women who are not pregnant Many of these
infections can be devastating to the fetus, and can lead to stillbirths,
miscarriages, and congenital anomalies The elderly have less robust immune
systems than younger adults overall, and several circumstances make them
even more susceptible to infections: 1 if they are frail with chronic
diseases; 2 if they have undergone chemotherapy for a malignancy this is
true for all age ranges, or 3 if they have a malignancy again, this is
true of all age ranges People with AIDS, people who take
immunosuppressive drugs
such as steroids, and people who have had
transplantation are at elevated risk for infection Finally, diabetes -
another epidemic disease in the US - also has a negative impact on
immunity, and infections are common in this group
People with AIDS People with AIDS are first infected with HIV, pass a
variable period of time infected but not yet damaged by the virus, and then
enter a period of profound susceptibility to infections AIDS after their
immune system has been weakened If they are not treated with one of the
modern cocktails of drugs that suppress the virus infection, they usually
die of infections How many people have AIDS, and where do they live?
First, the graph below shows the total number of prevalent cases of AIDS in
the US It can be seen that as AIDS death rates have gone down with modern
treatment the blue line, and as HIV positive people have not advanced to
AIDS as quickly as in the past yellow line, the total number of people
with AIDS has steadily increased orange line CDC AIDS Surveillance,
2001
This graph only shows people who have the HIV virus but who do not
have AIDS yet Generally, people double the number of cases of AIDS to get
an
approximation of the number of people who have HIV but have not yet
developed AIDS yet
The next graph shows AIDS rates by state double to include people
with HIV
What about where people with AIDS live, eg any rural versus urban
difference, or by state of residence? Again, double the rates quoted below
to include people with HIV
Adult/Adolescent AIDS Cases by Size of Place of Residence, Reported in 1999
and Cumulative, United States excluding Puerto Rico, US Virgin Islands,
Territories
| |1999 |1981 - 1999 |
|SIZE OF PLACE OF RESIDENCE |NUMBER |RATE PER |NUMBER |
| | |100,000 | |
| 500,000 |36,525 |266 |593,859 |
|50,000 - 500,000 |4,594 |120 |63,382 |
|NONMETROPOLITAN AREA |3,269 |74 |40,251 |
DATA FROM CDC, 2000C
Clearly, rural nonmetropolitan areas have a lower rate of AIDS
than do urban areas about a fourth, but some states, especially in the
Southeast, have high rural rates
of AIDS see following table While it
might have been said 10 or 15 years ago that there were few people with
AIDS residing in rural communities, this is no longer the case
AIDS Cases by Region and Size of Place of Residence Reported in 1999,
United States
| | 500,000 |50,000 - 500,000| 50,000 |
| |POPULATION | | |
|NORTHEAST N 14,006 |911 |58 |30 |
|NORTH CENTRAL N4337 |793 |118 |87 |
|SOUTH N 18,770 |716 |150 |117 |
|WEST N7,887 |900 |62 |38 |
DATA FROM CDC, 2000C
In 1999, most AIDS cases were reported from the South or the
Northeast Within each region, most cases are reported from large
metropolitan areas with population over 500,000 States in the North
Central region and the South reported the highest proportion of cases from
smaller metropolitan areas, and the majority of persons reported from non-
metropolitan rural areas 50,000 reside in the South
People living with AIDS, by
region of residence and year, 1993 through
1999, USA
|Region of Residence|1993 |1994 |1995 |1996 |1997 |1998 |1999 |
|Northeast |51,920 |59,545 |66,433 |73,674 |81,865 |88,867 |97,200 |
|Midwest |18,479 |20,398 |21,896 |23,764 |26,211 |28,310 |30,722 |
|South |58,857 |68,148 |75,635 |85,663 |97,376 |108,528|119,326|
|West |39,457 |43,031 |46,024 |49,739 |54,664 |59,164 |63,699 |
|US territories |5,742 |6,351 |6,807 |7,344 |8,126 |8,833 |9,332 |
|Total |174,475|197,471|216,796|240,184|268,242|293,702|320,282|
The estimated number of people living with AIDS is increasing in every
region of the country, as can be seen in the preceding table and in the
first graph in this section During 1993 to 1999, this number increased by
8357 CDC HIV/AIDS Surveillance 2000; table 23
Lastly, the CDC has estimated the total number of people living with
AIDS in non-metropolitan areas, which can act as a reasonable surrogate
for rural areas, to be 20,979 as of September 2000 CDC HIV/AIDS
Surveillance Supplemental Report 2000; table 5 This definition uses a cut-
off point
of the place of residence having 50,000 people Of this total,
15,350 people are aged 35-64, 4,994 are aged 19-34, 374 are 65 years of
age, 88 are teenagers, and 172 are children under the age of 13
Transplantation Solid organ and bone-marrow transplantations have
become increasingly common According to the International Bone Marrow
Transplant Registrys IBMTR Spring 2000 State of the Art Report,
approximately 47,000 bone marrow transplants were performed in 1998, of
which 28,000 were performed in North America The United Network for Organ
Sharing has published on its web site wwwunosorg the following data
regarding solid-organ transplants performed in the year 2000 Given the
rising number performed each year, a rough estimate of 50,000
transplantations per year is a reasonable figure
|Type of Transplant US data only |Number |
| kidney alone transplants 4,457 were living donors |13,372 |
|liver transplants |4,954 |
| pancreas alone transplants |435 |
| kidney-pancreas transplants |911 |
| intestine transplants
|79 |
| heart transplants |2,198 |
| heart-lung transplants |48 |
| lung transplants |956 |
| Total |22,953 |
People who have undergone transplantation are often required to
continue very significant immunosuppressive therapy for the rest of their
lives Median survival times for these individuals is increasing, and for
solid-organs may be as high as 80 at 5 years This suggests that the total
number of people living in the US after transplantation may be several
hundreds of thousands of people, perhaps an half million total Secure
estimates for the total number of transplantation survivors are not
available Where people live who have had a transplantation is not known
It is reasonable to assume that some proportion do live in rural areas
Chemotherapy Chemotherapy is a well-known risk factor for infectious
diseases, and chemotherapy damages the lungs, kidneys, liver, and other
organs It also damages normal cells as well as the
malignant cells it is
targeted to, so that it elevates the risk for subsequent cancers People
who are undergoing chemotherapy often have severely reduced immunity
Happily, this reduced immunity is usually time-limited, so that the immune
system tends to recover after the chemotherapy is over Because the
population is aging, both the incidence of cancer and the likelihood of
needing chemotherapy are elevated compared to the past Cancer is the
second leading cause of death in the US, and because most people with a
treatable cancer do undergo chemotherapy, chemotherapy is a common event
Exact estimates for the total number of people who undergo chemotherapy,
and their site of residence, are not available However, given that there
are about 540,000 deaths from cancer every year, and 12 million cases of
non-skin cancer diagnosed each year, it is likely that about 1 million
people begin chemotherapy each year, and about 45 of all those diagnosed
with cancer will eventually die of it Howe, 2001
Immunosuppressive therapy A number of medical illnesses are treated
by quieting the immune response Examples include arthritis, systemic lupus
erythematosis, inflammatory bowel disease,
and asthma Rheumatoid arthritis
and asthma are quite common - the former in adults, the latter in children
- and all of the above-mentioned diseases are often treated with steroids,
which indiscriminantly decrease immune function Rhematoid arthritis is
also now treated with more advanced immunosuppressive agents Asthma is now
considered to be epidemic in the
United States Between 1980 and the late 1990s, asthma incidence more than
doubled in the US, and is now reported in more than 5 of the total
population The first line of therapy for most individuals includes
bronchodilators, and then inhaled steroids While most people with asthma
do not undergo immunosuppression because of inhaled steroids, the sheer
number of people who must use these agents is very large, and a proportion
are immunocompromised
Diabetes Diabetes, like asthma, is now considered epidemic in the US
Approximately 800,000 new cases are diagnosed each year in the US Diabetes
directly affects the ability of the immune system to combat infections 80
of all men in the US are either overweight or
obese according to CDC criteria While only 016 of people under the age
of 20 have diabetes, 82 of those between 20
and 65 have the disease, and
184 of those aged 65 or older have diabetes CDC National Factsheet on
Diabetes, 1998 Deaths from pneumonia and influenza are much more common
in diabetics than in those without diabetes Diabetes also increases the
risk of heart disease, strokes, hypertenison, blindness, kidney disease,
nervous system damage, amputations, and dental disease In 1995, 98,872
people with diabetes had to begin dialysis or undergo kidney
transplantation, and about 67,000 amputations because of untreatable
infection or dry gangrene were conducted
Context:
Both legal and altruistic concerns have led to an interest in
preventing infections in immunocompromised sensitive
populations More than 100 people with AIDS and with cancer died
after the Milwaukee waterborne outbreak of cryptosporidiosis in
1993, highlighting the risk of this untreatable infection in
some people
Immunosuppressive conditions AIDS, chemotherapy, diabetes,
transplantation are increasing, as are some conditions that
require immunosuppressive treatment eg asthma
B33 Other groups that do or may constitute
sensitive subpopulations
Groups whose existing disease can be exacerbated by an exposure Other
adverse consequences that are NOT cancer or other malignancies include
effects such as hypertension, heart disease, and the like For example,
lead poisoning causes children to be anemic and decreases IQ, and causes
adults to be hypertensive Some heavy metals have particular actions on the
heart, kidney, or liver For a substance such as lead, a group that is
particularly susceptible to the effects of the lead would include
children or women who are already marginally anemic, or adult men with
marginal hypertension To give another example, arsenic is detoxified by
both the kidneys and the liver People with pre-existing diseases kidney
or liver disease or with congental defects eg a single kidney instead
of two will be at greater risk from a toxin that damages those organs or
that relies on that organ for detoxification A sensitive subpopulation for
a toxin that damages the heart would be a group with pre-existing heart
disease, for whom any additional cardiotoxic exposure might throw them into
heart failure or rhythm irregularity
Groups that have a genetic predisposition For
reasons which are not
well understood, some people develop specific diseases more frequently than
other people simply on the basis of their genetic background For example,
hypertension is more common in blacks, diabetes is very common in Native
Americans of the Pima tribe, cholera is more severe in people who are blood
group O positive, and gall bladder disease is more common in women than
men It is reasonable to believe this is because of differences in our
genetic make-ups It is also reasonable to believe that these genetic
differences will make some people more susceptible to the effects of some
water-borne contaminants Many toxins are rendered harmless by specific
enzymes in our bodies, and the degree to which these enzymes are present is
a direct function of our genetic background and the extent to which our
body is using these enzymes
Given the revolution occurring in our understanding of the genetic
makeup of humans, other animals, and bacteria, it is very likely that in a
few years medical scientists will be able to state with assurance that
people with a specific gene, or set of genes, are at increased risk of an
untoward consequence after exposure to a disease or
contaminant that may be
found in water For example, we already know that women with the brac gene
are at very high risk of breast cancer, whites are at elevated risk of
cystic fibrosis if they carry specific genes, and Native Americans lack
certain genes that allow for the rapid detoxication of alcohol
B4 The readers of this document are to be alerted that the explosion of
knowledge in this area is likely to lead to many more identified groups of
people who are unusually sensitive or susceptible to chemical, heavy metal,
or pathogenic water contaminants
The National Research Council, a constituent of the National Academies
of Science, has recently published its report entitled Classifying
Drinking Water Contaminants for Regulatory Consideration NRC, 2001 In
its report page 57, The committee recommends that the list of vulnerable
subpopulations described in the amended SDWA [Safe Drinking Water Act]
should not be seen as a minimum list, but rather as several examples of
possible vulnerable subpopulations A minimum list must go much further
than this In this regard, the EPA should considerwomen of childbearing
age, fetuses, the immunocompromised, people whose genetic
disposition makes
them more vulnerable to drinking water contaminants, people who are
exceptionally sensitive to an array of chemical contaminants, people with
specific medical conditions that make them more susceptible, and people
with poor nutrition As scientific knowledge about the determinants of
susceptibility expands, our ability to identify vulnerable subpopulations
will improve The Committee on Drinking Water Contaminants then went on
to state page 60 that The need to protect vulnerable subpopulations is
not only legally mandated by the amended SDWA, but also justified on equity
and environmental justice grounds The reports notes that the actual
definitions of who is in a sensitive subpopulation will not be solely
decided by scientific findings, but also on societal values and on viable,
democratic means of resolving policy dilemmas There are obvious policy
implications for the NRWA
C Which sensitive subpopulations are of concern to rural water providers?
All of them Why?
None of the groups discussed above only live in urban areas While
there may be differences between the relative proportions of these
subgroups between rural and urban areas, they
are only of degree
Legally, the EPA must examine the effects of regulations on sensitive
subpopulations implying that they cannot be dismissed from
consideration
It should be ethically supposed that people who live in rural areas
are just as deserving of good water as people who live in urban areas
and vice versa
All people move back and forth between states of sensitivity, moving
from a sensitive infancy, pregnancy, old age to a non-sensitive
subpopulation healthy adult throughout their lives
Water contaminants are generally of concern to multiple subgroups, and
NOT one, so that ignoring one particular group is unlikely to actually
reduce the need to be concerned about the contaminant For example,
Cryptosporidium is most linked to deaths in people with AIDS, yet it
kills infants via dehydrating diarrhea, and causes significant disease
and loss of work in other groups A chemical contaminant that has been
linked to cancer could affect children, pregnant women, and people who
have already had a cancer to a disproportionate extent
Rural regions are inhabited by people with:
1
infants
2 children
3 pregnant women
4 the elderly, both frail and well
5 people with AIDS
6 people with cancers
7 people who undergo chemotherapy
8 people with diabetes
9 people with rheumatoid arthritis, asthma, inflammatory bowel
disease, and other auto-immune disease that may require
immunosuppressive treatment
There are two arguments that can be made against considering some
sensitive subpopulations under specific circumstances The first is in the
case of transient noncommunity systems, where the period of exposure to
anything in the water is presumed to be short In this case, then acute
exposure risks that sensitive subpopulations experience are of greater
public health concern than are chronic exposure risks This is discussed
in more detail in Section E The second argument very small systems, where
the likelihood of a system providing water to a person with an unusual or
rare sensitivity would be quite low The difficulty with this second
argument is addressed in this next section
D Is it possible to know who belongs to a sensitive subpopulation?
Yes and no
Mechanisms already exist for people with
specific needs to receive
special delivery of water when there is a failure in the supply, eg
pregnant women and infants when there are nitrates in the water exceeding
the standards, and for people who are on dialysis Many communities have
arrangements to contact local medical care providers or others when
drinking water is not safe, so that these medical care providers can
contact specific sensitive individuals These mechanisms are not fail-safe,
but are very useful
One proposed answer to the issues raised by serving sensitive
subpopulations has been the concept of delivering two grades of water One
grade would be the standard grade, and the other perhaps delivered as
bottled water would be for sensitive subpopulations The difficulty lies
in peoples rights to privacy and confidentiality Many people face
discrimination because of being HIV seropositive or having AIDS, and they
are very unlikely to identify themselves to anyone who is not sworn to
secrecy Others might not want to let a public authority or water supplier
know they have cancer, diabetes, or some other thing that makes them part
of a sensitive subpopulation Pregnancy may be something that is hidden if
it is not a
condoned pregnancy A pregnant adolescent might be very
reluctant to have this information be public In contrast, it is hard to
imagine that a family would not tell a supplier that they had a baby, so
that the supplier could provide low nitrate water if need be Lastly,
delivery of water to an address might be the equivalent of a public
announcement of sensitivity, so some might balk at this remedy
It is possible that a water supplier could do an anonymous survey of
their community to ask if anyone has a condition that might render them
susceptible, but many people do not answer these surveys, and would have no
obligation to do so In addition, for small systems, it might still be
possible to guess who someone is, and such surveys would be confidential
only in name but not in practice
This author recommends that the NRWA not invest much effort in trying
to address concerns about sensitive populations by identification of the
sensitive so that they can receive some secondary water supply The
potential for lawsuits and for unintentional harm to come to people seems
very large; lists of the sensitive would have to be constantly updated and
protected from prying eyes; and from
a public relations viewpoint, could be
interpreted very negatively
E Nontransient and Transient Noncommunity Systems
Nontransient Noncommunity These systems serve important segments of the
population at a variety of locations, eg schools, and occasionally
hospitals It is obvious that systems that serve schools are serving
children and women of child-bearing age Systems that serve hospitals are
serving very ill people, many of whom have other illnesses or depressed
immune systems It is difficult to see how concerns about sensitive
subpopulations would not be brought to bear under these circumstances
Significant long-term drinking water ingestion occurs at other nontransient
noncommunity sites, such as offices and factories, and thus the same
concerns probably still hold
Transient Noncommunity These systems are defined as noncommunity systems
that do not supply the same population Last year, the Centers for Diseases
Control issued a report on waterborne disease outbreaks in 1997-1998 Most
of the outbreaks were associated with ground water supplies, many were
noncommunity, and all of the reported parasitic infections were
Cryptosporidium Barwick 2000
source:
Barwick 2000
Thus it is likely that there will be an impetus to include these water
systems in regulations that consider sensitive subpopulations Balancing
this impetus will be the fact that exposures to these water supplies are
generally brief and not sustained These circumstances suggest that the
major public health concern regarding transient noncommunity systems will
be to prevent acute exposures that could lead to harm, acknowledging that
the harms that could be due to chronic exposures are unlikely, since
these are by definition transient systems Exposures to infectious
organisms, and to elevated trihalomethane levels given the concerns
around reproductive risks, would be examples of the acute exposures one
would work to avoid In contrast, transient exposures to agents that
require chronic exposure to do harm might not bear the same public health
implications
F Appendix of a few useful public health concepts relevant to sensitive
subpopulations
Stopping exposure The whole discipline of public health arose from
the recognition that society could benefit by the identification of
specific hazards and then removing or reducing
them Public health operates
by identifying risks and removing them For adverse health events to occur,
the sensitive individuals or population must be exposed to the thing or
risks that are hazardous for them Thus, the clear intent of source water
protection, drinking water treatment, and the like is to reduce or
eliminate the chance that these people, as well as the general population,
will be exposed to these hazards Examples include the identification of
diarrheal diseases with contaminated drinking water in the 1800s, lung
cancer and smoking after World War II, and tuberculosis with raw milk Each
led to specific measures to reduce exposures of concern - eg water
treatment with chlorination and filtration, smoking cessation, and
pasteurization of milk
Acting upon suspicion When considering hazards and sensitive
subpopulations, it is important to understand some of the reasoning behind
public health protections Because we are talking about the health and well-
being of human beings, public health action is often taken when there is
only a suspicion that injury could arise Preventive actions or steps are
taken not only when it is certain that some harm could occur, they are
also
taken when there is a reasonable chance that the harm could occur Prudent
avoidance is justified as being better than taking care of problems after
they occur ounce of prevention is better than a pound of cure An
example of this is that pregnant women are not given medications that have
not been shown to be safe for them to take, because of the presumption that
some medications will cause harm to the fetus, such as birth defects or
even miscarriage Similarly, boil water advisories are often be issued
because water-quality indicators have deteriorated, rather than because
some group of people has already become ill This inevitably leads to
conflict with those who believe that preventive actions should be taken
only when the risk has been proven to exist
What is an increased risk? As a result of a comparison between the
likelihood of the event between the group of interest for example, young
children and the comparison group the whole population, it is found that
the likelihood is greater in the group of interest How does one talk of
increased risk? Either by stating an absolute rate or a comparative rate
An absolute rate is something like, 10 cases of pneumonia per
100,000
people, whereas a comparative rate is something like twice as likely to
occur in children than in adults Both are valid ways to discuss a risk
How significant is an increased risk? Significance is measured in
several ways First is the overall risk In common terms, being killed by
lightning is less common than being killed in an auto accident, so deaths
from auto accidents are more important or more significant than deaths
from lightning to society A second way to measure significance has to do
with the statistical meaning, which has to do with the confidence you have
that the increased or decreased risk is actually present From a
regulatory point of view, US law now states that susceptible or
sensitive populations must have their risks explicitly considered -
making their risks of significance to water suppliers
What is an adverse event or outcome? Something that is deleterious to
the person, like pain, discomfort, illness, lost work, decreased function,
decreased life-span, or death this list is obviously long Some adverse
events are self-limited, and others are permanent, making them more severe
or adverse It is sometimes nearly impossible to quantify exactly
how
severe an adverse outcome is eg, what is the value of a life, or a lost
limb, or 5 years of life-span, but is it usually possible to rank or order
adverse outcomes death is worse than a chronic disease than is a disease
that is temporary A variety of scales to rank adverse outcomes are
available, and each has its advantages or disadvantages
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———————–
[1] The EPA commissioned a workshop on definitions and research needs,
and more detailed discussions about how susceptibility is defined are
available in reports on the workshop Balbus 2000, Parkins 2000
———————–
Language from the Safe Drinking Water Act of 1996:
When proposing any national primary drinking water regulation that
includes a maximum contaminant level, the Administrator shall publish,
seek public comment on, and use an analysis of the quality and
extent of, the information, the uncertainties in the analysis supporting
subclauses I through VI [quantifiable and nonquantifiable
health risk
reduction, quantifiable and nonquantifiable costs, incremental costs and
benefits associated with each alternative maximum contaminant level
considered, effects of the contaminant on general population and sensitive
subpopulation, increased health risk as the result of compliance, including
risks associated with co-occurring contaminants] and factors with respect
to the degree and nature of the risk
The Director and the Administrator shall jointly establish a national
health care provider training and public education campaign to inform both
the professional health care provider community and the general public
about waterborne diseaseshall seek comment from interested groups and
individuals scientists, physicians, state local governments,
environmental groups, public water systems, and vulnerable populations
Copyright 2004 by National Rural Water Association Compilation copyright
2004 by National Rural Water Association All rights reserved No part of
this paper may be reproduced or transmitted in any form or by any means,
electronic or mechanical, including photocopying, recording, or by any
information storage and retrieval system, without
permission in writing
from the publisher
National Rural Water Association, 2915 South 13th Street, Duncan, OK 73533,
580-252-0629, FAX 580-255-4476
http://wwwnrwaorg, Printed in the United States of America
