Pathogens in Water: Value and Limits of Correlation with Microbial Indicators

Abstract

This article discusses the value and limitations of using microbial indicators to predict occurrence of enteric pathogens in water. Raw or treated sewage is a primary source of fecal contamination of the receiving surface water or groundwater; hence, understanding the relationship between pathogens and indicators in sewage is an important step in understanding the correlation in receiving waters. This article presents three different datasets representing different concentrations of pathogens and microbial indicators: sewage containing high concentrations of pathogens and indicators, surface water with variable concentrations, and groundwater with low concentrations. In sewage, even with very high levels of microorganisms, no mathematical correlation can predict the type or concentration of any pathogen. After discharge in the environment, direct correlation becomes biologically improbable as dilution, transport, and different inactivation rates occur in various environments. In surface waters, advanced statistical methods such as logistic regression have provided some level of predictability of the occurrence of pathogens but not specific counts. In groundwater, the continuous absence of indicators indicates an improbable occurrence of pathogen. In contrast, when these indicators are detected, pathogen occurrence probability increases significantly. In groundwater, given the nature and dissemination pattern of pathogenic microorganisms, a direct correlation with fecal microbial indicators is not observed and should not be expected. However, the indicators are still useful as a measure of risk. In summary, many pathogens of public health importance do not behave like fecal microbial indicators, and there is still no absolute indicator of their presence, only a probability of their co-occurrence.

Ecological and Public Health Implications of the Discharge of Multidrug-Resistant Bacteria and Physicochemical Contaminants from Treated Wastewater Effluents in the Eastern Cape, South Africa

“…Similarly, other studies have reported the detection of Vibrio in discharged effluents in South Africa and have emphasized the possibility of their survival in the environment [57][58][59][60]. The lack of statistical correlation between the abundance of FIB and potentially pathogenic Vibrio species points at the feeble attempt to use indicator organisms as surrogates for pathogens in water systems [61][62][63], while more reliable pathogen detection technology such as molecular-based and next-generation sequencing techniques will give more accurate results.…”

Effects of tillage and poultry manure application rates on Salmonella and fecal indicator bacteria concentrations in tiles draining Des Moines Lobe soils

“…Studies of human exposures have confirmed the increased risk of negative health outcomes from swimming in waters containing these and other fecal indicator bacteria (FIB) (Pruss, 1998). Alternative indicators, such as wastewater chemicals and genes unique to pathogenic bacteria, have been tested (Haack et al, 2009); however, despite the potential for regrowth and poor correlations to pathogens in some environmental settings (Field and Samadpour, 2007;Payment and Locas, 2011), EC and ENT have remained the preferred indicators for assessing the risk to human health (USEPA, 2012).…”

Biofilms Impact on Drinking Water Quality

“…• Faecal indicators are the best predictors of potential risks, but their concentrations rarely correlate perfectly with those of pathogens (Payment and Locas, 2011). Although in freshwater significant correlations have been established between faecal indices and pathogenic species, their presence in drinking water showed limited or no correlation with different species of pathogenic or opportunistic pathogenic bacteria, viruses, protozoa and fungi.…”