Indicators for Waterborne Pathogens (2004) / Chapter Skim
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2 Health Effects Assessment
2 Health Effects Assessment
Pages 53-108
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From page 53... ...
Furthermore, health effects assessment is discussed throughout this chapter in the context of drinking water and of fresh and marine recreational waters. This chapter also includes a description of the national surveillance system for waterborne disease outbreaks and several related epidemiologic studies currently being conducted.
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From page 54... ...
Health Effects Concerns and Early Studies of Microbial Water Quality Outbreak Investigations and Risk Estimates from Pathogen-to-Indicator Ratios in Water As discussed in Chapter 1, concerns about the sanitary quality of drinking water and the risks of enteric infectious diseases in the United States go back to at least the late 1800s, when enteric disease outbreaks were first recognized and linked at least tentatively to these exposure routes. Similar concerns for U.S.
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From page 55... ...
This approach has been used primarily for recreational waters and dates back to studies by Stevenson (1953) on Lake Michigan and the Ohio River.
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From page 56... ...
The measurement of indicators in the recreational water setting is typically conducted to determine if the level of contamination of surface waters such as oceans, lakes, and rivers is sufficiently elevated to pose a human risk and, therefore, to determine whether warnings should be issued or recreational waters should be closed to the public. In drinking water and food, philosophically a zero-tolerance approach has been taken for indicators.
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From page 57... ...
A microbial risk framework can be developed and used to understand the basic principles and data gaps in the study of public health risks associated with the characterization of recreational water quality using a variety of methodologies. Such an approach will lead to a decision support system for data gathering (types of data and methods)
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From page 58... ...
Of the epidemiologic studies, randomized controlled trials provide the strongest epidemiologic evidence of an etiologic association between exposure and outcome, followed in decreasing order by cohort studies, case-control studies, cross-sectional studies, and ecologic studies. Randomized Controlled Trial This epidemiologic experimental design is regarded as the most scientifically rigorous method of hypothesis testing available.
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From page 59... ...
They allow for the association of multiple health outcomes or diseases, or multiple endpoints within the progression of one disease, along with the exposure of interest. Like randomized controlled trials, cohort studies provide a temporal association between exposure and health outcome.
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As with most epidemiologic studies, cohort studies are subject to confounding. Known confounding factors can be controlled for in the analysis of the data, but unknown confounders are by their nature impossible to adjust for in the analysis.
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From page 61... ...
Longitudinal time series are cohort-type epidemiologic studies that correlate exposure variables of interest (e.g., an environmental indicator such as water turbidity or the presence of a waterborne pathogen like Cryptosporidium parvum in water) with health outcomes (e.g., a clinical measurement such as an immunologic marker of exposure in a serologic specimen or a direct measurement such as occurrence of diarrhea)
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U.S. National Waterborne Diseases Outbreak Surveillance System Surveillance for outbreaks associated with drinking water and recreational water has been going on since 1920 (Craun, 1986)
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. In addition, each drinking water system associated with an outbreak is classified by the following types of problems: untreated surface water, untreated groundwater, treatment deficiency (e.g., inadequate disinfection)
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. Usefulness of the Surveillance System Outbreak data gathered through this surveillance system are useful for identifying deficiencies in providing safe drinking water and recreational water, evaluating the adequacy of current regulations for water treatment, and monitoring water quality.
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From page 65... ...
Their findings suggested that the TCR is not able to identify those water systems that are vulnerable to an outbreak. The authors of that study suggest that source water be examined using a wide variety of indicators because simply monitoring treated drinking water for one indicator, most often coliforms, will not provide a useful measure of the water's overall microbial quality.
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. · Local and state health departments have limited budgets and allocate resources according to the perceived health risks to their communities.
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Epidemiologic Studies of Diseases Attributed to Drinking Water For drinking water, experimental and observational epidemiologic studies have focused on determining if there is an association between water consumption and adverse health outcomes, especially gastrointestinal illness. There has been an ongoing debate in the United States about the extent to which infectious diseases may be transmitted to humans through drinking water that meets federal standards for water quality.
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From page 68... ...
national estimate of waterborne disease occurrence. As noted in Chapter 1, the congressional language "waterborne disease occurrence" has been interpreted to mean that the focus of the study should be on "gastrointestinal disease attributable to municipal drinking water." A review of the epidemiologic studies that have and will provide data components (attributable fractions3 from select water systems and gastrointestinal rates in the general population)
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From page 69... ...
Despite the association of tap water with gastrointestinal illness, researchers did not find any correlations between illness and any of the physical, chemical, and microbial indicators measured. As the debate continued about whether coliform-free drinking water was also pathogen-free, Payment and colleagues followed up their first intervention trial with a second randomized trial in the same study area (Payment et al., 1997)
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From page 70... ...
The U.S. Intervention Trials and Observational Studies As mentioned previously, EPA and CDC decided that one method of developing a national estimate of endemic waterborne disease would be to obtain attributable fractions from controlled experiments and apply them to incident gastrointestinal illness rates in general populations determined from observational studies, such as cross-sectional surveys.
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. In addition, in preparation for this trial, a cross-sectional survey was conducted to determine the prevalence of gastrointestinal illness and drinking water consumption patterns in the HIV-infected study population.
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The objectives of this study were to determine whether rates of gastrointestinal illness were elevated during the flood and whether contact with flood water was associated with an increased risk of gastrointestinal illness. The results of this study have been accepted for publication in the American Journal of Epidemiology (Deborah Levy, CDC, personal communication, 2004)
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From page 73... ...
Attributable fractions obtained in the intervention trials will be applied to these population rates. Population-based estimates of the burden of gastrointestinal illness in the United States calculated from FoodNet 1996-1997 data were published in 1999 and again in 2002 (Herikstad et al., 2002; Mead et al., 1999)
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From page 74... ...
(2003) used time series analyses to study the association between emergency room visits and hospitalization caused by gastrointestinal illness and drinking water turbidity before and during the Milwaukee waterborne Cryptosporidium outbreak of 1993 (see also Chapter 1)
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From page 75... ...
The study design proposed was a 12-month, double-blinded, randomized intervention trial that will include 900 households and will measure rates of gastrointestinal illness in groups with drinking water that receives different levels of treatment. The national estimate of endemic waterborne disease will be updated and refined as data become available from the ongoing as well as new studies and additional data sources are mined (Deborah Levy, CDC, personal communication, 2004)
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76 INDICATORS FOR WATERBORNE PATHOGENS TABLE 2-2 Summary of Key Characteristics of Select Epidemiologic Studies Associating Drinking Water with Health Outcomes Geographic Study Sponsor/ Location -- Study Primary Institution Study Design Water System Population Size National Institutes Randomized Sonoma and Elderly 500 of Health/ triple-blinded Santa Rosa, households University of intervention California- California, trial mixed water Berkeley system CDC/Tufts Longitudinal Lowell and Newton, Children 1,000+ persons University time series Massachusetts -- per city surface water systems, one with filtered river water and one unfiltered from a partially protected watershed CDC/Tufts Cohort study Lowell and Newton, Children 400 University Massachusetts -- households surface water systems, one with filtered river water and one unfiltered from a partially protected watershed EPA Community Undisclosed city, General 300 intervention Massachusetts -- population households trial before and surface water after installation system of a filtration plant EPA Community Seattle, Washington Children and 300 intervention -- surface water elderly households trial before system and after installation of a filtration plant with ozonation
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From page 77... ...
Water quality Cryptosporidium exposures and measured by turbidity antibodies in outcomes over and presence of serum and saliva time Cryptosporidium specimens, and oocysts in finished episodes of water gastrointestinal illness Consumption of Prevalence of Relative risk and Data analysis ongoing tap water and Cryptosporidium correlations of exposure to antibodies in exposures and recreational serum and saliva outcomes water. Water specimens, and over time quality measured episodes of by turbidity and gastrointestinal presence of illness Cryptosporidium oocysts in finished water ICR data on source Seroprevalence of Attributable Study completed, results water monitoring Cryptosporidium fraction not published antibodies and episodes of gastrointestinal illness before and after the intervention ICR data on Seroprevalence of Attributable Study completed, source water Cryptosporidium fraction AWWARF report monitoring antibodies and (Project #2367)
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From page 78... ...
Linking gastrointestinal illness with water consumption is not the epidemiologic equivalent of linking the illness to waterborne pathogens and indicators despite the intuitive understanding that the two hypotheses are closely related. Data collection efforts in outbreak investigations of drinking water have concentrated mostly on identifying the epidemiologic link to water consumption and identifying a pathogen in clinical specimens rather than in water samples.
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From page 79... ...
In addition, the Big WET study did not show an association between drinking water and illness and it remains to be seen if any of the secondary analyses when linked to the water quality data collected in the nested study will provide measurable epidemiologic associations. To have adequate statistical power to address the epidemiologic association of health outcomes with specific indicators and waterborne pathogens, the study sample size must be large, and therefore the costs can become prohibitively expensive.
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From page 80... ...
Because of the recognized deficiencies of previous studies (see also Chapter 1) , EPA conducted prospective epidemiologic-microbiological studies in the 1970s to compare rates of gastrointestinal illness in swimmers and beach-going non-swimmers at fresh and marine beaches differing in microbial water quality and sources of fecal contamination.
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From page 81... ...
These values were based on risk levels of 8 and 19 gastrointestinal illnesses per 1,000 swimmers at freshwater and marine beaches, respectively, and they were estimated to be equivalent to the risk levels for criteria of 200 fecal coliforms per 100 mL. These pivotal studies by EPA prompted numerous epidemiologic-microbiological studies of similar and improved design in many parts of the world (see Table 2-3 and systematic review of these and other recreational water studies by Wade et al., 2003)
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Figure 2-1 presents the relationship between indicator organism density in marine water and illness risk for bathers. A similar compilation of the results for studies in fresh recreational waters is shown in Figure 2-2.
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83 lines Solid Reprinted, Note: SOURCE: waters.
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84 with indicate lines Reprinted, Solid Note: SOURCE: waters.
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From page 85... ...
. Based on analyses of data from numerous studies on the relationships between swimming-associated health effects and the microbial quality of bathing water, the WHO and other international as well as national entities have concluded that fecal streptococci and enterococci currently are the fecal indicator microorganisms that best predict health risks in recreational waters (WHO, 2001)
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to identify likely health risks (WHO, 2001, 2003)
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From page 87... ...
From these studies, a subset was found to be amenable to the determination of relative risk of a health outcome, such as gastrointestinal, respiratory, skin, ear, or eye effects. For gastrointestinal illness, several indicators showed significant associations with the levels of the following indicators in recreational water: fecal streptococci (enterococci)
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additional rigorously conducted epidemiologic studies such as observational studies that have standardized definitions of exposure and health outcomes and standardized methods, as well as randomized trials to establish etiology; 5. additional studies using enteric viruses and bacteriophages as water quality indicators; 6.
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From page 89... ...
. QUANTITATIVE MICROBIAL RISK ASSESSMENT Historically, as noted throughout this report, acceptable microbial levels for evidence of pathogen risk in drinking water, contact recreational waters, and shellfish harvesting waters have been set using indicator organisms, most often the coliform (either total or fecal)
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From page 90... ...
Alternative but similar protocols have been published -- for example, by the International Life Sciences Institute (ILSI, 1996, 2000) -- that are specifically designed to apply to waterborne pathogens.
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From page 91... ...
Thus, the assessment of exposure, and dose-response with microorganisms must consider this intrinsic sampling and exposure variability, while chemical risk assessment can ignore this phenomenon. · For microorganisms, there is strong biological information to indicate that as few as one microorganism has the potential to cause harm (Haas et al., 1999b)
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From page 92... ...
and drinking water; two case studies for drinking water exposure are described below. Risk from Ingestion of Giardia in Drinking Water Using data from human volunteer studies, Regli et al.
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From page 93... ...
Acceptance by International Organizations In the field of water quality, WHO has recently developed an overall framework for guideline and standard setting in all of its water-related activities-including drinking water, recreational water, and exposure to effluents and sludges from the agricultural use of such materials -- using microbial risk assessment as a foundation (Fewtrell and Bartram, 2001)
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From page 94... ...
. Outside the water field, microbial risk assessment has increasingly been adopted both in the United States and internationally as a paradigm for developing standards for food safety.
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From page 95... ...
For example, a drinking water outbreak of Giardia showed a graded response between attack rate and self-reported glasses of water consumed (Istre et al., 1984)
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From page 96... ...
However, as described earlier, the concentration of a pathogen in water at the point of exposure that would be allowed as an "acceptable risk" is likely to be much lower than can be practically and reliably detected, as with finished drinking water (Regli et al., 1991; Rose et al., 1991a,b)
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. From these investigations, the direct health risk from exposure to microbially contaminated recreational water can be determined as a function of a dose metric in terms of indicator concentrations in the water.
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From page 98... ...
SUMMARY: CONCLUSIONS AND RECOMMENDATIONS Health effects assessments for waterborne pathogens can be based on a number of approaches. Each approach has strengths and weaknesses, and all have been or are being used to document and quantify the health risks of microbes in water.
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Under the SDWA Amendments of 1996, recently completed (though largely unpublished at the time this report was finalized) epidemiologic studies of drinking water and endemic disease have focused on establishing associations between water consumption and gastrointestinal illness.
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· Additional epidemiologic studies are needed to look at the association between water consumption and gastrointestinal illness in groundwater systems, and to correlate water quality data (pathogens and indicators) with health outcomes.
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. · Additional epidemiologic studies should be conducted to determine the occurrence of chronic/recurrent disease attributable to waterborne pathogens in habitual users of recreational waters (e.g., surfers)
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2002. Participant blinding and gastrointestinal illness in a randomized, controlled trial of an in-home drinking water inter vention.
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1996. Cryptosporidiosis: An outbreak associated with drinking water despite state-of-the-art water treatment.
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2001. A randomized, blinded, controlled trial investigating the gastrointestinal health effects of drinking water quality.
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2000. Estimating the infection risk in recreational waters from the faecal indicator concentration and from the ratio between pathogens and indicators.
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1997. A prospec tive epidemiological study of gastrointestinal health effects due to the consumption of drinking water.
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2000. Drinking water turbidity and gastrointestinal illness in the elderly of Philadelphia.
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From page 108... ...
Do U.S. Environmental Protection Agency water quality guidelines for recreational waters prevent gastrointestinal illness?
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