at Greatest Risk of Waterborne Disease
A. Reynolds, Ph.D.
The risk of waterborne disease is clearly recognized by the general public,
but perhaps not as earnestly by immunocompromised individuals as it should
be. This group-consisting primarily of the very young, the elderly, pregnant
women and persons with diminished immunity, either due to medical intervention
(organ transplants, invasive surgery), previous illness (diabetes, cancer)
or infection (AIDS, etc.). For these populations, the risk of serious
illness due to contaminated water consumption is greater than the general
Guidelines issued by the
U.S. Environmental Protection Agency (USEPA) and the Centers for Disease
Control & Prevention (CDC) recommend that immunocompromised individuals
drink only treated water and, whenever possible, boil their water prior
to consumption. Because microbial infections are more likely to have fatal
outcomes with persons of decreased immunity, the water purification industry
has an immense responsibility to those most at risk.
State of sensitive populations
According to 1991 estimates from the Department of Commerce, sensitive
populations constitute nearly 20 percent of the population (see Table
1). Future projections indicate that a continued increase in population
growth and advances in medicine will lead to a greater number of individuals
The number of individuals
over the age of 65 is expected to be up to 69.4 million by 2030.1 During 1995, the proportion of
adults aged greater than or equal to 65 years was 12.8 percent, compared
with an anticipated 20 percent during 2030. Adults aged greater than or
equal to 85 years are the fastest growing segment of the population; during
1995-2030, their numbers are projected to increase from 3.6-to-8.5 million.
Conversely, approximately 21.5 million children greater than or equal
to four years of age will be in living in the United States by 2025.2
In 1999 alone, 1,221,800
new cancer cases are estimated to have occurred.3 Calculations using projected populations and
assuming constant prevalence rates yield an estimated 6.2 million people
with a history of cancer in the United States by the year 2000 and 9.6
million by 2030.4
Due to highly active antiviral
therapy repelling the onset of AIDS with HIV positive individuals, there's
been a decrease over previous years, with 44,296 new cases reported in
the United States in 1998.5 The number of people living with AIDS, however,
is increasing as new treatments prolong the lives of infected persons.
In 1997, approximately 270,000 people were living with AIDS.6
As of Jan. 15, 66,067 patients
were waiting for organ transplants. More than 21,197 transplants were
performed in 1998.7
Although the causative agent is not identified in half of all documented
U.S. waterborne outbreaks, a number of microbial agents have been found
to cause waterborne outbreaks (see Table 2). Protozoa and viruses
are most commonly associated with waterborne illness.8 The severity of the outcome following
exposure to human pathogens is affected by a number of factors including
general health and immune response, nutrition, age, and other nonspecific
In addition, specific characteristics
of the infecting organism play a major role. For example, some viruses
primarily produce disease in children, but only affect a small percentage
of adults. Most enteric pathogens will produce clinically observable illness
in 50 percent or more of infected individuals.9,10 This means the other 50 percent of the infected population
will not show visible signs of illness. For immunocompromised individuals,
the infectivity rate may be much higher. In addition, the number of clinical
illnesses leading to death is higher for sensitive populations.
Recent outbreaks of waterborne
disease have certainly had the most deleterious effects on immunocompromised
individuals. For instance, on Aug. 28, 1999, a massive E. coli
outbreak occurred in Albany, N.Y. Labeled the worst outbreak in the state's
history, the number of people reporting symptoms was 921, with 65 hospitalized.
The waterborne organism also claimed the life of a three-year-old girl
and a 79-year-old man.9 The
well publicized Milwaukee, Wis., outbreak linked to Cryptosporidium
was reported to have affected 403,000 individuals. More than 100 deaths
among immunocompromised individuals were associated with that incident.10
Assessing risk by group
PregnancyDuring pregnancy, women
appear to be at greater risk of enteric virus infection and subsequent
infection to the unborn fetus. Available information on Hepatitis E infections-no
U.S. outbreaks have been reported-in immunocompetent and pregnant women
show that the case fatality ratio is 1-to-2 percent vs. 10-to-20 percent,
respectively. A viral infection during pregnancy may result in transfer
to the child either in utero, during birth or shortly after birth. Enterovirus
infections may be particularly dangerous in the first two weeks of an
infant's life, where infection is most likely to result in a fatal outcome.
Coxsackie B viruses have been associated with stillbirths, spontaneous
abortions and birth defects.11
Nursing home residentsMicrobial
outbreaks in nursing homes have been documented as having a significantly
higher mortality than the general population.11 Case fatality rates may be 10-to-100 times greater than
the general population, depending on the agent. One documented outbreak
of rotavirus in a nursing home resulted in nearly 66 percent infection
with symptomatic illness, an extremely high attack rate.11
Cancer and transplant
patientsCancer patients and transplant recipients are subjected
to intensive therapies known to reduce the ability of the immune system
to ward off disease. The mortality rate among bone marrow transplant patients
with enteric viral infections was an alarming high 59 percent according
to one study.11
AIDS patientsEnteric diseases are among
the most common and devastating problems affecting AIDS patients. Estimates
of 50-to-90 percent of AIDS victims suffer from chronic diarrheal illnesses.
Adenovirus and rotavirus are the most common enteric viruses afflicting
persons with AIDS. Twelve percent of the AIDS patients with clinical symptoms
are infected with adenovirus, and 45 percent of these cases will result
in death within two months.11
Cryptosporidium is perhaps the most serious microbe
affecting AIDS patients, usually resulting in a prolonged diarrhea with
fluid losses of several liters a day. Mortality rates are as high as 50
percent.11 The CDC and USEPA have issued guidance statements informing
immunocompromised individuals on how to minimize or avoid Cryptosporidium
infection (see Chart 1), in light of the fact the protozoan pathogen
is difficult to remove from water and that public water supplies do not
provide adequate measures of protection for sensitive populations.
Some water treatment systems,
particularly reverse osmosis (RO) units, have been associated with regrowth
of heterotrophic plate count bacteria (HPC). Although the majority of
heterotrophic bacteria are not pathogenic to humans, some strains are
opportunistic pathogens, meaning they can cause disease in immunocompromised
populations. Thus, the CDC recommends boiling as the most effective treatment
for the reduction of microbes in water.
As a health conscious industry, we must continue to educate sensitive
populations to the fact that public drinking water supplies, even when
they meet or exceed all state and federal standards, are not sterile;
nor is bottled water or water treated by a home water treatment device.
According to a CDC draft report, "Immunocompromised persons who wish
to take independent action to reduce the risk of waterborne cryptosporidiosis
may choose to take precautions similar to those recommended during outbreaks
(such as boiling tap water for one minute). Such decisions should be made
in conjunction with their health care provider."
For more information,
visit the following websites:
for Disease Control and Preventionwww.cdc.gov
U.S. Census Bureauwww.census.gov
United Network for Organ Sharingwww.unos.org
American Cancer Societywww.cancer.org
The CDC manual, Cryptosporidium
and Water: A Public Health Handbook, also can be downloaded at: www.cdc.gov/ncidod/emergplan/27appendix.htm
1. Centers for Disease Control and Prevention, "Surveillance for
morbidity and mortality among older adultsUnited States, 1995-1996,"
Morbidity and Mortality Weekly Report, 48 (SS08): 7-25, 1999.
2. U.S. Census Bureau, "Population pyramid summary for United States,"
online reference (updated Dec. 29, 1999): http://www.census.gov/ipc/www/idbpyr.html
3. American Cancer Society, Cancer Facts and Figures, Atlanta, Ga., 1999.
4. CDC, "Progress in Chronic Disease Prevention: The Prevalence of
Cancer-Connecticut," Jan. 1, 1982, Morbidity and Mortality Weekly
Report, 36(13): 205-207, 1987.
5. CDC, HIV/AIDS Surveillance Supplemental Report, 5(1):1-14, 1999a.
6. CDC, HIV/AIDS Surveillance Supplemental Report, 5(3):1-12, 1999b.
7. United Network for Organ Sharing, "Critical data: U.S. facts about
transplantation," online reference (updated Jan. 15, 2000): www.unos.org/newsroom/critdata_main.htm#transplants
8. CDC, "Waterborne and foodborne disease outbreaks," Morbidity
and Mortality Weekly Report, 39:1-57, 1990.
9. CDC, "Public Health Dispatch: Outbreak of Escherichia coli O157:H7
and Campylobacter Among Attendees of the Washington County Fair, New York,
1999," Morbidity and Mortality Weekly Report, 48(36): 803, 1999c.
10. Kramer, M.H., et al., "Surveillance for Waterborne-Disease Outbreaks-United
States, 1993-1994," Morbidity and Mortality Weekly Report, 45 (SS-1):
11. Gerba, C.P., J.B. Rose and C.N. Haas, "Sensitive populations:
Who is at the greatest risk?" International Journal of Food Microbiology,
30: 113-123, 1996.
A. Reynolds is a research scientist at the University of Arizona with
a focus on the development of rapid methods for detecting human pathogenic
viruses in drinking water. She is also a member of the WC&P Technical
1. Number of immunocompromised individuals, United States
home or other care facility
SOURCE: U.S. Census
2. Enteric microbes known to cause waterborne outbreaks
Escherichia coli O157:H7
from Gerba, Rose, Haas, "Sensitive Populations,"
1. Language and Water Barriers: Official Advice from the CDC
least a minuteis the best extra measure to ensure that water
is free of the waterborne pathogen Cryptosporidium and other potentially
harmful organisms. Filtered water or bottled water may also be
effective, provided a specific treatment protocol has been followed.
Look for the following information on the label of filters or
designed to remove Crypto should have any of the four messages
below on a package label:
labeled only with these words may not be designed to remove Crypto:
Reverse osmosis (with or without NSF testing)
Absolute pore size of 1 micron or smaller (with
or without NSF testing)
Tested and certified by NSF Standard 53 for cyst
Tested and certified to NSF Standard 53 for cyst
Nominal pore size of 1 micron or smaller
One micron filter
Effective against Giardia
Effective against parasites
EPA approved (Caution: EPA does not approve or test
EPA registered (Caution: EPA does not register filters
for Crypto removal)
Filters collect germs from your water, so someone who is not HIV
infected should change the filter cartridges for you; if you do
it yourself, wear gloves and wash your hands afterwards. Filters
may not remove crypto as well as boiling does because even good
brands of filters may sometimes have manufacturing flaws that
allow small numbers of crypto to get past the filter. Also, poor
filter maintenance or failure to replace filter cartridges as
recommended by the manufacturer can cause your filter to fail.
water* labeled as follows was processed by methods effective against
water* labeled solely as follows may not have been processed by
methods effective against Crypto:
| Reverse osmosis treated
Filtered through an absolute 1-micron or smaller filter
Bottled water labels reading well water, artesian
well water, spring water, or mineral water
do not guarantee that the water does not contain Crypto.
However, water that comes from protected well or protected spring
water sources is less likely to contain Crypto than bottled
water or tap water from less protected sources, such as rivers
Home distillers are also effective at removing Crypto
and other germs from your water. If you use one, you need to carefully
store your water as recommended for storing boiled water.
Crypto is killed or removed in canned or bottled
soda, seltzer and fruit drinks; coffee or tea at 175°C or
hotter; and pasteurized drinks.
Fountain drinks; fruit drinks made with tap water; iced
tea or coffee; and unpasteurized juices or fresh juices may be
contaminated with Crypto.
Excerpted from a handbook provided by the CDC entitled "Cryptosporidium
and Water: A Public Health Handbook," from the Working Group
on Waterborne Cryptosporidiosis, Atlanta, GA.