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MICROBES IN DRINKING WATER: RECENT EPIDEMIOLOGIC RESEARCH TO ASSESS WATERBORNE RISKS
Citation:
Calderon, R L. MICROBES IN DRINKING WATER: RECENT EPIDEMIOLOGIC RESEARCH TO ASSESS WATERBORNE RISKS. Presented at Second International Conference on the Safety of Water Disinfectin: Balancing Chemical and Microbial Risks, Miami Beach, FL, 11/15-17/1999.
Description:
Microbial caused diarrhea continues to be a major cause of death in many countries. The transmission of these organisms to humans is often mediated by drinking water. These enteric illnesses occur in epidemic form (the occurrence of disease in excess of normal expectancy) and in endemic form (the normal prevalence of a disease) . Epidemic illnesses associated with waterborne microbes are referred to as waterborne disease outbreaks. Waterborne disease outbreak surveillance has and continues to be useful for identifying emerging pathogens, important deficiencies in source water quality, drinking water treatment and distribution system integrity. The degree to which waterborne outbreaks are recognized and investigated, varies from community to community. The surveillance or reporting of a waterborne disease outbreak is a very passive system in the United States. The 1995-1996 biennial report of waterborne disease outbreaks reported 22 drinking water outbreaks.
Endemic gastroenteritis associated with waterborne pathogens has been a recent area of new epidemiologic innovation. Endemic illness is either studied from a symptomatic identification standpoint (generic illness, etiologic agent rarely known) or from an organism specific standpoint. The types of questions and subsequent study designs for organism-specific versus general endemic illness can be very different. The Centers for Disease Control in the United States has been conducting a cross-sectional study of symptomatic diarrhea in seven states (representing approximately 12% of the U.S. population). This recent study estimated that there were 340 million episodes of diarrhea in the United States on an annual basis.
Serological epidemiology is the use of antibody response in determining the prevalence or incidence of a microbial specific illness in a population. Recent studies of Cryptosporidium antibody in outbreak and non-outbreak situations have suggested that in some communities the drinking water supply may be the most common source of Cryptosporidium. Seroepidemiology of Cryptosporidium has been reported in the UK, Italy, Australia, Canada and the United States.
Intervention studies are done on a population basis where the investigator through intervention at the individual level or at the community level attempts to evaluate strategies for decreasing exposure to microbes in drinking water. Individual or household interventions have been completed in Canada (2) and in Australia. One study is underway and two are planned for the U.S. Community intervention studies are accomplished much in the same way a household intervention studies except that the intervention is at the community level such as upgrade in treatment (unfiltered to filtered) or a change in disinfection (chlorine to ozone/chlorine combination). As in the household intervention studies, families are monitored over a period of time only; in this case families are monitored before the change and after the change. The goal being to evaluate the difference in illness rates. An added benefit of community intervention studies is that since the entire community is changing, other surveillance systems can be evaluated such as clinical laboratories, hospital admissions, nursing homes, school absentees or pharmaceutical sales of over the counter anti-diarrheals. In the U.S. an unfiltered community changing to a filtered community has been completed and two others are planned.
A final study design that will be discussed is the use of time series analysis in correlating water quality parameters with some surveillance index of diarrheal illness. Two recent studies in the U.S. have reported correlations of hospital admissions for diarrhea with turbidity measurements of water collected at the water treatment plant. As with the wealth of air pollution studies these studies are very difficult to interpret.
In summary, in the years since the last international conference several new study designs have been applied toward the issue of microbial contamination of drinking water. These along with the standard outbreak investigations have contributed to our understanding of water in the transmission of microorganisms.