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February 2002: Volume 44, Number 2

Children at Increased Risk of Waterborne Contamination
by Kelly A. Reynolds, MSPH, Ph.D.

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All age groups across the globe are impacted by the quality of water. Likewise, all ages are impacted by drinking water outbreaks; however, children are more likely to suffer greater attack rates, more serious illness and mortality from infectious diseases than other populations.

Epidemiological studies have been conducted to evaluate the relative incidence of gastroenteritis among consumers of tap water vs. those drinking tap water filtered by reverse osmosis (RO), designed to remove waterborne pathogens.1 Children who drank non-filtered tap water suffered a greater incidence of gastrointestinal disease. In another study, families were provided with purified bottled water, tap water bottled at the treatment plant, and tap water from the same plant that was delivered through the distribution system.2 Those consuming the bottled tap water were 14 percent more likely to become ill than those drinking purified bottled water. Even worse, drinking tap water from the home tap resulted in 19 percent greater illness. An evaluation of children from 2-5 years old shows an even more dramatic difference with an excess of illness in 17 percent of those consuming bottled tap water and 40 percent of those drinking water from the tap. This study, and many others, contributes to the mounting evidence that the young need additional safeguards against infectious disease.

Contributing factors of risk
Although children consume less water than adults, they’re more adversely affected by waterborne viruses, primarily due to their immature immune system. The immune system is the first line of control for the body against invading microbes. Children under the age of two, in particular, have impaired spleen, B-lymphocyte, and T-cell helper function—important mechanisms for the prevention of microbial infections.

Levels of Immunoglobulin A, an essential compound for combating microbial infections in the gastrointestinal tract, are drastically reduced in children, with adults having 70-to-300 times that of newborns. Even at 10 years of age, the levels are half that found in healthy adults. Stomach acids and other antimicrobial secretions are also reduced in children compared to adults. Similar trends have also been shown to occur in animal studies comparing neonate and adult mice. In addition to the physical deficiencies for microbial attack, children often have poor habits of hygiene, resulting in greater exposure to microbes from a variety of environmental sources, and not only limited to drinking water. The lack of frequent and effective handwashing is a major concern as well as children’s routine hand-to-mouth or surface-to-mouth contact.

Post-infection, infants and young children are more susceptible to serious dehydration. In addition, their neurological, heart and endocrine systems are more likely to be affected compared to older children and adults. The adverse impact to any of these systems can result in serious illness, hospitalization and even death.

It’s only diarrhea
The impact of gastrointestinal illness, also referred to as GI, cannot be underestimated. Diarrhea is the second most common illness in the United States, surpassed only by respiratory infections. Worldwide, over 500 million episodes of diarrhea occur each year in children under the age of five. Six million of these infections result in death, making diarrhea the leading cause of infant mortality. Although the majority of these deaths are in developing countries, diarrhea is still listed as one of the top 10 leading causes of death in infants in the United States, where an estimated 21-to-37 million episodes occur annually in children under the age of five. More than 200,000 of these children are hospitalized and up to 400 die of the disease each year.

Serious enteric infections can be transmitted to a child at birth from an infected mother. Studies show that pregnant women consume more tap water than other adults, potentially placing themselves at increased risk, if the tap water were contaminated. The immunity of children can, however, be improved by the nursing mother. Breast-feeding is known to compensate for immune deficiencies in children. Breast-fed infants have been found to harbor significantly higher concentrations of antibodies (markers of immune response to microbes) compared to formula-fed infants. Diarrheal disease incidence tends to be half as prevalent in breast fed babies compared to those formula fed. The length of time an infant is breast fed also has an impact on their immunity, with infants nursed for three months or less developing respiratory and gastroenteric infections earlier than those nursed for longer periods. In general, proper nutrition is vital to prevent enteric infections, as malnutrition is directly associated with an increased susceptibility to gastrointestinal illness.

Impact of viral agents
Enteric viruses are the major cause of childhood gastroenteritis in the United States and are the leading identifiable cause of childhood hospitalizations for gastroenteritis, resulting in an estimated 150 deaths each year. In over 79 percent of hospital admissions for gastrointestinal illness are due to unknown causes, while greater than 25 percent are due to viruses, approximately 5 percent due to bacteria and less than 0.3 percent due to parasites. Rotavirus alone is associated with more than 16 percent of all diarrhea-associated hospital admissions.

Many enteric viruses are spread by the waterborne route including rotavirus, adenovirus, caliciviruses, Norwalk virus, astrovirus, hepatitis A and E, and enteroviruses. More than half of the enteric virus infections result in mild or asymptomatic illness; however, they can cause a wide range of serious and even life-threatening illnesses in children (see EXTRA).

Treatment and prevention
Treatment for viral infections is limited primarily to supportive therapy. The replacement of lost fluids and electrolytes is imperative to prevent complications from dehydration. In addition, bismuth subsalicylate has been shown to result in a faster recovery in some instances. Vaccines are available for Hepatitis A and poliovirus. A rotavirus vaccine was licensed by the Food and Drug Administration in 1998 but has been pulled from the market due to a possible association with a rare intestinal disorder.

Overall, children and other immunocompromised persons bear the greatest burden of illness associated with waterborne viruses. Not only are they more likely to become infected but they’re also more likely to become ill, suffer more severe symptoms and die more often than adults and healthier populations. The best defense against viral infections is prevention. In many cases, exposure to infectious viruses can be minimized by practicing good hygiene and proper treatment of water supplies. When available, vaccines have proven effective for the drastic decline of many infectious diseases.

Finally, regulatory agencies have recognized the disproportionate impact of waterborne disease in children and have begun to address the concern under a 1996 revision of the Safe Drinking Water Act, requiring that populations at greatest risk be taken into consideration in the development of future rules. In 1997, President Bill Clinton signed an executive order, ”Protection of Children from Environmental Health Risks and Safety Risks,” as a primary directive to federal agencies to evaluate the impact of planned actions on the health and safety of children. These efforts are reinforced by a USEPA policy requiring that infants and children be considered in risk assessment analyses used for regulatory decisions and standards development.

Conclusion
Studies have shown that children consuming municipal water, which has been treated with RO filtration designed to remove microbes, had a substantial reduction of their risk of gastrointestinal illness from water. RO and other point-of-use systems, designed for removal of infectious organisms, promise to provide additional measures of safety for children consuming treated and untreated drinking water.

References
1. Payment, P., et al., “A randomized trial to evaluate the risk of gastrointestinal disease due to consumption of drinking water meeting current microbiological standards,” American Journal of Public Health, 81, 703-8, 1991.

2. Payment, P., et al., “A prospective epidemiology study of gastrointestinal health effects due to the consumption of drinking water,” International Journal of Environmental Health Research, 7, 5-31, 1997.

About the author
Dr. Kelly A. Reynolds is a research scientist at the University of Arizona with a focus on development of rapid methods for detecting human pathogenic viruses in drinking water. She holds a master of science degree in public health (MSPH) from the University of South Florida and doctorate in microbiology from the University of Arizona. Reynolds also has been a member of the WC&P Technical Review Committee since 1997.

EXTRA: A Watchlist for Children

Rotavirus
It has been responsible for several drinking water outbreaks worldwide and is the major cause of childhood gastroenteritis. The incidence of disease peaks in the fall and winter months. Nearly 30 percent of children under the age of 2 show evidence of infection; although half of these cases experience no notable illness. By the age of 3, most children are thought to have been infected by rotavirus. Infections are common in both developed and developing countries.

Adenovirus
Its incidence may be as high as 12 percent around the world. Known to spread by the fecal-oral route, drinking water outbreaks with this virus have been suspected but not documented. Infections via the waterborne route have included recreational water exposures. Adenovirus 40 and 41 are identified as a common cause of acute viral gastroenteritis. They’re only present in the gastrointestinal tract and are extensively distributed, suggesting that water may be a route of transmission.

HAV
Hepatitis A virus (HAV) is well established as a waterborne virus. Most infections in children are asymptomatic with increasing attack rates in older children (>10 years old) and adults. The virus is relatively hardy, able to survive for days to months in different types of water. In almost half of the HAV cases, the route of transmission cannot be identified. In developing countries, most of the population is exposed in early childhood, a condition that results in increased immunity in older individuals.

HEV
In developing countries, Hepatitis E virus (HEV) may be endemic with incidence rates as high as 14 percent. Although children become infected, the illness is most serious in adults. Infection is most serious in pregnant women where the mortality rate ranges from 20-to-40 percent. HEV outbreaks haven’t been reported in the United States but animal reservoirs have been found. Unlike HAV, early infection of this virus doesn’t appear to infer lasting immunity.

Astrovirus
Astrovirus infections occur year round with a peak in the winter and spring months. They tend to cause mild illness and have been associated with drinking water outbreaks. They have high prevalence rates among children in developed and developing countries. By the age of 4, 64 percent of children show evidence of infection with astrovirus, increasing to 87 percent by the ages of 5-10.

Enteroviruses
The enterovirus group includes coxsackie viruses, echo viruses, polio viruses and other enterovirus strains. They’re associated with a broad spectrum of diseases, including meningitis, herpangina, hand-foot-mouth disease, conjunctivitis, myocarditis, febrile illness and others. The infection rate of enteroviruses among children is almost twice that of adults. These viruses peak in the summer and fall months, with symptomatic infections approaching 78 percent for those under age 4. Not clearly associated with drinking water outbreaks, the primary transmission route of these viruses is unknown. Recreational water exposures have been documented.

Norwalk and caliciviruses
Without cultural methods to grow Norwalk and caliciviruses, their true incidence is difficult to assess. Numerous drinking water outbreaks have been linked to these viruses, with several occurring in elementary schools and children’s camps. Although children and adults experience the same attack rates, secondary transmission of Norwalk virus is greater among school-aged children. It’s estimated that over a billion dollars a year is allocated for the Norwalk virus illnesses in the United States with nearly a half-billion dollars due to waterborne transmission.