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. 2005 Jun;71(6):3163-70.
doi: 10.1128/AEM.71.6.3163-3170.2005.

Validity of the indicator organism paradigm for pathogen reduction in reclaimed water and public health protection

Valerie J Harwood  1 , Audrey D Levine, Troy M Scott, Vasanta Chivukula, Jerzy Lukasik, Samuel R Farrah, Joan B Rose
Affiliations

Validity of the indicator organism paradigm for pathogen reduction in reclaimed water and public health protection

Valerie J Harwood et al. Appl Environ Microbiol. 2005 Jun.

Abstract

The validity of using indicator organisms (total and fecal coliforms, enterococci, Clostridium perfringens, and F-specific coliphages) to predict the presence or absence of pathogens (infectious enteric viruses, Cryptosporidium, and Giardia) was tested at six wastewater reclamation facilities. Multiple samplings conducted at each facility over a 1-year period. Larger sample volumes for indicators (0.2 to 0.4 liters) and pathogens (30 to 100 liters) resulted in more sensitive detection limits than are typical of routine monitoring. Microorganisms were detected in disinfected effluent samples at the following frequencies: total coliforms, 63%; fecal coliforms, 27%; enterococci, 27%; C. perfringens, 61%; F-specific coliphages, approximately 40%; and enteric viruses, 31%. Cryptosporidium oocysts and Giardia cysts were detected in 70% and 80%, respectively, of reclaimed water samples. Viable Cryptosporidium, based on cell culture infectivity assays, was detected in 20% of the reclaimed water samples. No strong correlation was found for any indicator-pathogen combination. When data for all indicators were tested using discriminant analysis, the presence/absence patterns for Giardia cysts, Cryptosporidium oocysts, infectious Cryptosporidium, and infectious enteric viruses were predicted for over 71% of disinfected effluents. The failure of measurements of single indicator organism to correlate with pathogens suggests that public health is not adequately protected by simple monitoring schemes based on detection of a single indicator, particularly at the detection limits routinely employed. Monitoring a suite of indicator organisms in reclaimed effluent is more likely to be predictive of the presence of certain pathogens, and a need for additional pathogen monitoring in reclaimed water in order to protect public health is suggested by this study.

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Figures

FIG. 1.
FIG. 1.
Mean indicator organism and pathogen concentrations in untreated wastewater and disinfected effluent from six wastewater reclamation facilities (n = 30). Log10 concentrations of bacterial indicators (CFU · 100 ml−1), coliphages on E. coli 15597 and E. coli 700891 (PFU · 100 ml−1), enteric viruses (MPN · 100 liters−1), Giardia total counts (cysts · 100 liters−1), and Cryptosporidium total and viable counts (oocysts · 100 liters−1) are shown. Detection limits were used as concentrations for parameters that were nondetectable. The boxes represent 50% of the data, the vertical lines represent the mean, the lines extending from the boxes represent the 95% confidence limits, and the individual data points represent outliers.
FIG. 2.
FIG. 2.
Relationship between detection of individual indicators and accuracy of pathogen detection in disinfected effluent. All percentages were calculated from the total sample number. Detection limits were 0.2 CFU · 100 ml−1 for total and fecal coliforms, enterococci, and Clostridium perfringens and 10 PFU · 100 ml−1. for coliphages. (A) Enteric viruses; (B) Giardia cysts; (C) Cryptosporidium oocysts; (D) infectious Cryptosporidium.
FIG. 3.
FIG. 3.
Discriminant analysis, with results showing the percentage of samples correctly categorized with respect to presence or absence of each pathogen. All of the indicators were used as binary dependent variables. Present, percentage of samples with pathogens actually present and in which pathogen presence was predicted by DA. Absent, percentage of samples in which pathogens were not detected and in which pathogen absence was predicted by DA.
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