Appendix 1C1: Indicator Organisms

This appendix provides further background information about indicator organisms and EPA's review of epidemiological studies. For a more complete discussion, refer to EPA's Implementation Guidance for Ambient Water Quality Criteria for Bacteria (USEPA, 2000).

1. Organisms That Can Indicate Fecal Contamination
2. EPA's Review of Recent Epidemiological Studies
3. References

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1. Organisms That Can Indicate Fecal Contamination

Because many pathogens are not easily detected, indicator organisms are a fundamental monitoring tool used to measure both changes in environmental (water) quality or conditions and the potential presence of hard-to-detect target pathogenic organisms. An indicator organism provides evidence of the presence or absence of a pathogenic organism surviving under similar physical, chemical, and nutrient conditions. For fecal contamination, indicator organisms should (Sloat and Ziel, 1992; Thomann and Mueller, 1987):

• Be easily detected using simple laboratory tests.
• Generally not be present in unpolluted waters.
• Appear in concentrations that can be correlated with the extent of contamination.
• Have a die-off rate that is not faster than the die-off rate of the pathogens of concern.

Indicator bacteria are usually harmless, more plentiful, and easier to detect than pathogens (Wilhelm and Maluk, 1999). Methods are not currently available to culture or enumerate all the disease-causing organisms that might be present in natural waters. For example, viruses and protozoans are generally not used as indicators because of difficulties associated with isolating them and detecting their presence in environmental samples. The bacteria species chosen as indicators are indigenous to the intestines of warm-blooded animals and indicate the potential presence of dangerous pathogens that can cause human illnesses.

Use and reliability are two factors that states and tribes should consider when selecting a pathogen indicator. The lack of correlation between certain indicators and pathogen-caused diseases in humans, as well as the uncertain relationship between indicators and different sources of pathogens, is a limitation of bacterial indicators. A positive result for the indicator organism means that the indicator is present in the waterbody, not necessarily that waterborne pathogens are also present. The presence of an indicator might not indicate whether those pathogens (if present) are viable or capable of causing disease and whether the source of the contamination is humans or other animals.

Indicators vary in their ability to reliably predict potential risks to human health. Some indicators have been shown to have a greater statistical relationship to disease than others. Also, currentdisease from other pathogens that can cause skin, upper respiratory tract, eye, ear, nose, and throat disease (USEPA, 1999). More research on the use of other bacteria and viruses as indicators is being conducted at the federal, state, and local levels. Despite variability in the ability of indicators to reliably predict potential risks to human health, EPA studies indicate that enterococci and E. coli are the most effective available primary indicators for predicting the presence of gastrointestinal illness-causing pathogens, and for marine waters, enterococci is most appropriate.

One area of current scientific debate is whether indicator bacteria react differently under various climatic and environmental conditions. Preliminary evidence suggests that E. coli and enterococci can be detected at tropical locales such as Puerto Rico, Hawaii, and Guam in waters where there is no apparent source of contamination from warm-blooded animals (USEPA, 1999). EPA and others are evaluating whether the current indicator bacteria grow and persist in natural tropical environments. If E. coli and enterococci are determined to propagate naturally in tropical conditions, EPA will conduct additional research to identify alternative indicators for tropical areas.

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2. EPA's Review of Recent Epidemiological Studies

Since the publication of EPA's 1986 criteria, a number of studies related to bacterial indicators have been completed. Therefore, EPA reviewed relevant recent studies to determine whether the studies continue to support EPA's recommendation to use E. coli and enterococci as bacterial water quality indicators. EPA's review focused on the epidemiological studies that related swimming-associated health effects to marine and freshwater bacterial water quality using studies performed after 1984. (For a complete discussion of these studies, see EPA's Implementation Guidance on Water Quality Criteria for Bacteria, USEPA, 2000).

EPA's Office of Research and Development (ORD) concluded:

The epidemiological studies conducted since 1984, which examined the relationships between water quality and swimming-associated health effects, have not established any new or unique principles that might significantly affect the current guidance EPA recommends for maintaining the microbiological safety of marine and freshwater bathing beaches. Many of the studies have, in fact, confirmed and validated the findings of the U.S. EPA studies. There would appear to be no good reason for modifying the Agency's current guidance for recreational waters at this time (Dufour, 1999).

The new studies added an additional body of evidence that supports EPA's 1986 criteria. As a result of this examination, EPA determined that its 1986 water quality criteria for bacteria continue to represent the best available science and serve as a defensible foundation for protecting public health from gastroenteritis in recreational waters. EPA found no reason to undertake a revision of the criteria at that time (USEPA, 2000).

The following table includes the relevant findings of the research EPA reviewed that has been conducted on indicator organisms since 1986.

Table 1. Summary of Research Conducted Since 1986

Researcher/Year/ Location	Type of Water	Microorganisms Evaluated	Relevant Findings
Fattal et al. (1987) Israel	Marine	Fecal coliforms Enterococci Escherichia coli	Of the indicators tested, enterococci were the most predictive indicator for enteric disease symptoms.
Cheung et al. (1990) Hong Kong	Marine	Fecal coliforms E. coli Klebsiella spp. Enterococci Fecal streptococci Staphylococci Pseudomonas aeruginosa Candida albicans Total fungi	Of the indicators tested, E. coli showed the highest significant correlation with combined swimming-associated gastroenteritis and skin symptom rates.
Balarajan et al. (1991) United Kingdom	Marine	Unknown	Risk of illness increased with degree of exposure.
Von Schirnding et al. (1992) South Africa (Atlantic Coast)	Marine	Enterococci Fecal coliforms Coliphages Staphylococci F-male-specific   bacteriophages	Uncertainty about the sources of fecal contamination may explain the lack of statistically significant relationship rates of illness between swimmers and nonswimmers.
Corbett et al. (1993) Sydney, Australia	Marine	Fecal coliforms Fecal steptococci	Gastrointestinal symptoms in swimmers did not increase with increasing counts of fecal bacteria. Counts of fecal coliforms were better predictors of swimming-associated illness than streptococci.
Kay et al. (1994) United Kingdom	Marine	Total coliforms Fecal coliforms Fecal streptococci Pseudomonas aeruginosa Total staphylococci	Compared to the other indicators tested, fecal streptococci were the best indicator of gastrointestinal symptoms.
Kueh et al. (1995) Hong Kong	Marine	E. coli Fecal coliforms Staphylococci Aeromonas spp. Clostridium perfringens Vibrio cholera Vibrio parahemotylicus Salmonella spp. Shigella spp.	No statistical relationship between E. coli and swimming-associated illness was found (possibly because only two beaches were sampled).
Fleisher et al. (1996) United Kingdom	Marine	Total coliform Fecal coliform Fecal streptococci Total staphylococci Pseudomonas aeruginosa	Nonenteric illness can be transmitted through recreational contact with marine waters contaminated with sewage.
Haile et al. (1996) California, USA	Marine	Total coliforms Fecal coliforms Enterococci E. coli	The association of symptoms with both E. coli and fecal coliforms was very weak
McBride et al. (1998) New Zealand	Marine	Fecal coliforms E. coli Enterococci	Enterococci were most strongly and consistently associated with illness risk for the exposed groups. If swimmers remained in the water for more than 30 minutes, the risk differences were significantly greater between swimmers and nonswimmers.
Seyfried et al. (1985) Canada	Fresh	Fecal coliforms Fecal streptococci Heterotrophic bacteria Pseudomonas aeroginosa Total staphylococci	A small correlation was observed between fecal streptococci and gastrointestinal illness.
Ferley et al. (1989) France	Fresh	Fecal coliforms Fecal streptococci	The best relationship is between fecal streptococci and gastrointestinal illness.
Francy et al. (1993) Ohio, USA	Fresh	E. coli Fecal coliforms	In this study, the relationship between E. coli and fecal coliform bacteria was found to be statistically significant. This relationship can differ from one data source to another.

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References

1. Balarajan, R., V. Soni Raleigh, P. Yuen, D. Wheeler, D. Machin, and R. Cartwright. 1991. Health risks associated with bathing in sea water. British Medical Journal 303:1444-1445.
2. Cheung, W.H.S., K.C.K. Chang, R.P.S. Hung, and J.W.L. Kleevens. 1990. Health effects of beach water pollution in Hong Kong. Epidemiological Infections 105:139-162.
3. Corbett, S.J., G.L. Rubin, G.K. Curry, D.G. Kleinbaub, and Sydney Beach Users Study Advisory Group. 1993. The health effects of swimming at Sydney beaches. American Journal of Public Health 83(12):1701-1706.
4. Dufour, A.P. 1999. Memo from A. Dufour to Elizabeth Sutherland, Acting Director, Standards and Applied Science Division, U.S. Environmental Protection Agency, Office of Science and Technology.
5. Fattal, B., E. Peleg-Olevsky, T. Agursky, and H.I. Shuval. 1987. The association between seawater pollution as measured by bacterial indicators and morbidity among bathers at Mediterranean bathing beaches of Israel. Chemosphere 16:565-570.
6. Ferley, J.P., D. Zmirou, F. Balducci, B. Baleux, P. Fera, G. Larbaigt, E. Jacq, B. Moissonnier, A. Blineau, and J. Boudot. 1989. Epidemiological significance of microbiological pollution criteria for river recreational waters. International Journal of Epidemiology 18(1):198-205.
7. Fleisher, J.M., D.Kay, R.L. Salmon, F.Jones, M.D. Wyer, and A.F. Godfree. 1996. Marine waters contaminated with domestic sewage: Nonenteric illnesses associated with bather exposure in the United Kingdom. American Journal of Public Health 86(9):1228-1234.
8. Francy, D.S., D.N. Myers, and K.D. Metzker. 1993. Escherichia coli and Fecal-Coliform Bacteria as Indicators of Recreational Water Quality. Water Resources Investigations Report 93-4083.U.S. Geological Survey, Columbus, OH.
9. Haile, R. 1996. A Health Effects Study of Swimmers in Santa Monica Bay. Santa Monica Bay Restoration Project, Monterey Park, CA.
10. Kay, D., J.M. Fleisher, R.L. Salmon, F. Jones, M.D. Wyer, A.F. Godfree, Z. Zelenauch-Jacqotte, and R. Shore. 1994. Predicting likelihood of gastroenteritis from sea bathing: Results from randomised exposure. The Lancet 344(October 1):905-909.
11. Kueh, C.S.W., T-Y Tam, T.W. Lee, S.L. Wang, O.L. Lloyd, I.T.S. Yu, T.W. Wang, J.S. Tam, and D.C.J. Bassett. 1995. Epidemiological study of swimming-associated illnesses relating to bathing-beach water quality. Water Science Technology 31:1-4.
12. McBride, G.B., C.E. Salmond, D.R. Bandaranayake, S.J. Turner, S.J. G.D. Lewis, and D.G. Till. 1998. Health effects of marine bathing in New Zealand. International Journal of Environmental Health Research 8:173-189.
13. Seyfried, P.L., R.S. Tobin, N.E. Brown, and P.F. Ness. 1985. A prospective study of swimmingrelated illness: II. Morbidity and the microbiological quality of water. American Journal of Public Health 75(9):1071-1075.
14. Sloat, S., and C. Ziel. 1992. The Use of Indicator Organisms to Assess Public Water Safety. Hach Company, Loveland, CO.
15. Thomann, R.V., and J.A. Mueller. 1987. Principles of Surface Water Quality Modeling and Control. Harper and Row, New York.
16. USEPA. 1999. Action Plan for Beaches and Recreational Waters. EPA 600/R-98-079. U.S. Environmental Protection Agency, Office of Research and Development and Office of Water, Washington, DC.
17. USEPA. 2000. Implementation Guidance for Ambient Water Quality Criteria for Bacteria—1986. Draft. January 2000. EPA 823/D-00-001. U.S. Environmental Protection Agency, Office of Water, Washington, DC.
18. Von Schirnding, Y.E.R., R. Kfir, V. Cabelli, L. Franklin, and G. Joubert. 1992. Morbidity among bathers exposed to polluted seawater. South African Medical Journal 81(6):543-546.
19. Wilhelm, L.J. and T.L. Maluk. 1999. Fecal-Indicator Bacteria in Surface Waters of the Santee River Basin and Coastal Drainage, North and South Carolina, 1995-1998.

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