Indicators for Waterborne Pathogens (2004) / Chapter Skim
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4 Attributes and Application of Indicators
4 Attributes and Application of Indicators
Pages 164-195
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From page 164... ...
INDICATOR ATTRIBUTES For almost 40 years, Bonde's (1966) attributes of an ideal indicator have served as an effective model of how a fecal contamination index for public health risk and treatment efficiency should function (Box 4-1)
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From page 165... ...
Biological Attributes The most important biological attribute is a strong quantitative relationship between indicator concentration and the degree of public health risk. This relationship has been demonstrated primarily through epidemiologic studies for recreational exposures (Cabelli et al., 1979; Cheung et al., 1990; Seyfried et al., 1985a,b; Zmirou et al., 1987)
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From page 166... ...
-- Shock proteins and other biochemical survival strategies °Response to disinfectants · Similar (or greater) transport to pathogens °Filtration °Sedimentation or settling °Adsorption to particles · Present in greater numbers than pathogens · Specific to a fecal source or identifiable as to source of origin BOX 4-3 Desirable Attributes of Methods · Specificity to desired target organism °Independent of matrix effects · Broad applicability · Precision · Adequate sensitivity · Rapidity of results · Quantifiable · Measures viability or infectivity · Logistical feasibility °Training and personnel requirements °Utility in field °Cost °Volume requirements
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From page 167... ...
However, exceptionally long survival of potential indicators, such as spore-forming Clostridium perfringens, may render them too overprotective or nondiscriminatory because they may be present at concentrations mistakenly considered to be indicative of a health risk long after the pathogens have declined to levels not considered a risk. The next desirable attribute is that the indicator be present at densities that are detectable with an easily sampled volume.
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From page 168... ...
Many waters that are tested for microbiological quality are saline, or turbid, or have a high organic content, all of which have the potential to interfere with some indicator measurement methods (Geldreich, 1978)
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From page 169... ...
Logistical feasibility will often govern the indicator method of choice. Cost concerns can be important when large numbers of samples are needed for screening purposes, but they may be less important when the consequences to be addressed have major impacts on human health risk, such as the risk of an outbreak
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From page 170... ...
When a standard is exceeded, actions are taken to reduce exposure, such as increased treatment levels for drinking water, shellfish bed closures, or warnings to avoid recreational water contact. Because drinking water warning systems focus on treatment effectiveness, which is largely outside the scope of this study, this section focuses on the recreational contact warning system.
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From page 171... ...
There is zero tolerance for fecal coliforms or Escherichia coli in treated drinking water, the presence of which is considered compelling evidence of unacceptable health risk requiring immediate action. How ever, background levels of microorganisms from natural sources have to be accounted for in monitoring ambient water systems.
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From page 172... ...
Recent reviews of beachgoer epidemiology studies (Prüss, 1998; Wade et al., 2003) found that enterococci had the best relationship to health risk among presently used indicators for marine water, but less than half of the studies found a significant health relationship and the dose-response curves establishing the relationship between increased illness and indicator density were highly variable.
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From page 173... ...
. A major problem with present water contact warning systems is that bacterial indicator concentrations are spatially and temporally variable and most sampling is too infrequent to transcend this granularity.1 Taggart (2002)
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From page 174... ...
close a beach because of a perceived health risk or (2) do nothing.
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The first is to decide whether a health warning should be issued because a recreational water body closure is typically issued only after determining that a human fecal source is associated with the high bacterial indicator levels. The second is to identify the most promising approach for fixing the problem.
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From page 176... ...
Source identification is then achieved through matching the patterns produced by bacteria obtained in ambient water samples to those in the database. The most frequently used phenotypic method is multiple antibiotic resistance profiling (MAR; Cooke, 1976; Hagedorn et al., 1999; Harwood et al., 2000; Parveen et al., 1997)
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From page 177... ...
The phenotypic source identification methods have the advantage of rapid processing of multiple samples, relatively low cost per sample, and use of equipment already present in most microbiological laboratories. Recently, the detection of specific antibiotic resistance traits in enteric bacteria found in environmental media and fecal waste sources has been used to identify bacterial sources without the development of an extensive reference database of isolates.
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From page 178... ...
Direct Measurement Approach Direct measurement of certain bacteria or viruses that are exclusive to human waste or are rarely found in animals is another approach that has been used to distinguish human from animal sources of fecal contamination (though see Box 4-6)
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From page 179... ...
the microbe indicative of human waste input. A number of direct measurement indicators have been used for microbial source tracking as described below and summarized in Table 4-3: · Bifidobacterium spp.
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fragilis HSP40 Possibly human specific Not always present in sewage or bacteriophage present in low numbers Not always human specific, depending on bacterial strain and geographic location F+ RNA bacteriophage Groups are correlated with Lower numbers in warm marine and sources (humans versus tropical waters due to variable animals and livestock) with survival rates small % of overlap Human enteric viruses Human specific if cell cultures Low concentrations in water and and genome targets to other samples amplify are chosen carefully Better cultivation and molecular Addresses hazard identification methods needed component of risk assessment paradigm Rhodococcus coprophilis Specific indicator of grazing Detected by culture for a lengthy animal fecal sources period (weeks)
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From page 181... ...
They found statistical significance in the assignment of serotypes to specific human or animal sources, but the distinction may not be as definitive as previously thought since there was some overlap between the serotypes and their expected animal sources. · Human enteric viruses are potentially definitive for human fecal contamination and have been monitored directly in water since the 1960s.
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From page 182... ...
Status and Trends Assessment Bacterial indicators are frequently used in ambient water quality monitoring to assess whether water bodies meet state-designated water quality standards for beneficial use(s) , such as drinking water supply, water contact recreation, and shellfish harvesting (see also footnote 3, Chapter 1)
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From page 183... ...
The source tracking techniques discussed above are appropriate to these applications. In addition, most marine assessments are still based on coliforms, even though enterococci have been found to be more closely associated with health risk and significantly more marine water bodies would be detected as impaired if enterococci were used instead of coliforms (Noble et al., 2003b)
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From page 184... ...
that will require monitoring for Escherichia coli by utilities with surface source drinking water supplies (EPA, 2002b, 2003; see also Chapter 1 and Table 1-1)
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From page 185... ...
The known risks from viruses in fecally contaminated groundwater, combined with evidence that coliphages are better indicators of viruses than are indicator bacteria, and that human enteric viruses are detectable in fecally contaminated groundwater using current technologies, suggest that coliphage or direct virus monitoring would enhance the assessment of groundwater microbiological quality and would make better indicators of human health risk (see Chapter 6 for further information)
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From page 186... ...
Another predictive-based warning system, which operates on a longer time scale, involves land use as an indicator of fecal contamination. Many recreational bathing areas, drinking water sources, and shellfishing areas are located in drain
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The most important biological attribute is a strong quantitative relationship between indicator concentration and the degree of public health risk. One of the most important method attributes is its specificity, or ability to measure the target indicator organism in an unbiased manner.
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From page 188... ...
Several factors limit the effectiveness of current recreational water warning systems, the most prominent of which is the delay in warnings caused by long laboratory sample processing times. Current laboratory measurement methods used to enumerate indicator bacteria (multiple tube fermentation, membrane filtration, and chromogenic substrate)
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From page 189... ...
techniques on the horizon that should be incorporated into monitoring systems when they have been adequately validated. Public health risk from exposure to fecally contaminated water is likely to vary depending on whether high indicator concentrations resulted from animal or human sources, and microbial source tracking tools will allow public health managers to incorporate that distinction into their decision making.
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Applied and Environmental Microbiology 67: 1494-1502. Cheung, W.H.S., R.P.S.
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2003. National Primary Drinking Water Regulations: Long Term 2 Enhanced Surface Water Treatment Rule; Proposed Rule.
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2000. Classification of the antibiotic resistance patterns of indicator bacteria by discriminant analysis: Use in predicting the source of fecal contamination in subtropical Florida waters.
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2002. Development of Source-Specific Indicator Organisms for Drinking Water (Project #2645)
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From page 194... ...
2001. Enterovirsuses detected by reverse transcriptase polymerase chain reaction from the coastal waters of Santa Monica Bay, California: Low correlation to bacterial indicator levels.
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From page 195... ...
Swimming-associated health risk. American Journal of Public Health 75: 1068 1070.
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