Waterborne disease outbreaks in the United States of America: causes and prevention.

National statistics on waterborne outbreaks in the United States of America show that 1,702 waterborne outbreaks with 542,018 cases of illness and 1,089 deaths have been reported. Almost all deaths prior to 1940 were due to typhoid fever; 9 deaths from other causes have occurred since 1971. During the past decade, 291 waterborne outbreaks were reported in community (43%) and noncommunity (33%) systems, and from the ingestion of contaminated water from recreational (14%) and individual (10%) water sources. Although several large waterborne outbreaks occurred during the past decade, most were in small communities. The number of illnesses per outbreak in noncommunity systems during the past decade is much larger than that reported during any previous period, and the magnitude of these outbreaks indicates the potential effect on the travelling, transient population. During 1981-1990, contaminated, untreated groundwater or inadequately disinfected groundwater was responsible for 43% of all reported waterborne outbreaks, and contaminated, untreated surface water or inadequately treated surface water was responsible for 24% of all reported outbreaks. The use of untreated groundwater has declined in importance as a cause of outbreaks, and more outbreaks are now caused by inadequate or interrupted disinfection of groundwater. The increased occurrence of outbreaks in disinfected groundwater systems may be due to (i) increased use of disinfection with little effort to reduce or eliminate sources of contamination, and (ii) not providing effective, continuous disinfection. In surface-water systems, outbreaks occur primarily because of inadequate or interrupted disinfection in systems that do not provide filtration, but a large increase in outbreaks has recently occurred in filtered systems.(ABSTRACT TRUNCATED AT 250 WORDS)