Waterborne Diseases

In the mid-1800s, physician John Snow recommended removal of the handle from a water pump in a London neighborhood, ending an outbreak of cholera that had killed more than 500 people in a 10-day period. In the past 150 years, much progress has been made in understanding and preventing the transmission of infectious waterborne diseases. Even so, waterborne pathogens continue to be transmitted to humans via recreational water contact and contaminated drinking water supplies throughout the world, resulting in morbidity and mortality that is preventable. Infections that result from contact with waterborne pathogens can result in either endemic or epidemic disease. Most waterborne diseases are endemic in a population—there is some baseline level of disease that occurs normally in a population. An epidemic is defined when cases occur in excess of the normal occurrence for that population.

The Centers for Disease Control and Prevention (CDC) estimates that each year infectious waterborne diseases account for approximately 2 billion episodes of diarrhealeadingtoanestimated1milliondeathsworldwide. Most of these diarrheal deaths occur among children in developing countries, but the elderly and immunocompromised populations are also at an increased risk for waterborne infections. Table 1 lists the primary agents of infectious waterborne disease worldwide. These bacteria, viruses, and protozoa typically cause gastrointestinal symptoms, although some may cause a variety of other health effects, including neurological disorders (e.g., primary amoebic meningoencephalitis caused by Naegleria fowleri) and respiratory illness (e.g., pneumonia caused by Legionella species.

The CDC reports biennial estimates of waterborne outbreaks attributed to bacteria, viruses, and protozoa in the United States. In 2001 and 2002, 31 drinking water outbreaks were reported in 19 states, resulting in 1,020 cases of illness. Sixty-five recreational water outbreaks were reported by 23 states, resulting in 2,536 cases of illness. The number of cases from recreational and drinking water outbreaks for selected pathogens is shown in Table 2. Endemic waterborne disease is more difficult to quantify, but the 1996 Amendments to the Safe Drinking Water Act mandated that the U.S. Environmental Protection Agency (EPA) and the CDC jointly develop a national estimate of waterborne disease occurrence in the United States. Preliminary estimates by the EPA indicate that of all cases of acute gastrointestinal illness occurring in the U.S. population served by community water systems, approximately 8.5% may be attributed to their drinking water (∼ 16.4 million cases per year).