Concentrations Of Indicator Organisms Research Articles

A model for prediction of microbial disease burden of water supply options in Bangladesh

Infectious diseases caused by microbial pathogens are most common and widespread health risks are associated with drinking water. This paper presents a model for prediction of disease burden for ingestion of microbial pathogens through drinking water in rural Bangladesh. The concentration of indicator organisms (Thermotolerant coliform or Escherichia coli) in cfu/100ml were taken as input in the model and estimated disease burden in ?DALYs with some relevant statistical parameters are obtained as output. The model has been found useful in quantifying relative disease burden of microbial pathogens, comparing safety of different water supply options and delineating the interventions needed to reduce disease burden from drinking water. DOI: http://dx.doi.org/10.3329/sjm.v4i1.22759 Stamford Journal of Microbiology, Vol.4(1) 2014: 31-36

Estimating the correlation between concentrations of two species of bacteria with censored microbial testing data

Indicator organisms, such as generic Escherichia coli (GEC) and coliforms, can be used to measure changes in microbial contamination during the production of food products. Large and consistent reductions in the concentration of these organisms demonstrates an effective and well-controlled production process. Nevertheless, it is unclear to what degree concentrations of indicator organisms are related to pathogenic organisms such as Campylobacter and Salmonella on a sample-by-sample basis. If a strong correlation exists between the concentrations of different organisms, then the monitoring of indicator organisms would be a cost-effective surrogate for the measurement of pathogenic organisms. Calculating the correlation between the concentrations of an indicator and pathogenic organism is complicated because microbial testing datasets typically contain a large proportion of censored observations (i.e., samples where the true concentration is not observable, with nondetects and samples that are only screen-test positive being examples). This study proposes a maximum likelihood estimator that can be used to estimate the correlation between the concentrations of indicator and pathogenic organisms. An example based on broiler chicken rinse samples demonstrates modest, but significant positive correlations between the concentration of the indicator organism GEC when compared to the concentration of both Campylobacter and Salmonella. A weak positive correlation was also observed between concentrations of Campylobacter and Salmonella, but it was not statistically significant.

Hygienic quality of faeces treated in urine diverting vermicomposting toilets

On-site sanitation solutions have gained much interest in recent years. One such solution is the urine diverting vermicomposting toilet (UDVT). This study evaluated the hygienic quality of the composted material in six UDVTs in operation in France. Samples were taken from three sampling positions in each toilet, with increasing distance from the fresh material. The concentration of Salmonella spp., Enterococcus spp., thermotolarent coliforms and coliphages were analysed and plotted against a number of variables. The variables found to have the greatest impact was the pH (for Enterococcus spp. and thermotolarent coliforms (TTC)) and time since last maintenance (coliphages). The pH was found to correlate with the material maturity. The current practise of maintenance can cause recontamination of the stabilised material and increase the risk of regrowth of pathogenic microorganisms. A modification in the maintenance procedure, in which a fourth maturation point is introduced, would eliminate this risk. UDVTs were found to be a good on-site sanitation option as the maintenance requirement is small and the system effectively reduced odour and concentration of pathogen and indicator organisms in human waste while keeping the accumulation of material down to a minimum. If the vermicompost is to be used for crops consumed raw, an additional sanitisation step is recommended.

Absence of Direct Association between Coliforms and Escherichiacoli in Irrigation Water and on Produce

Irrigation water is considered a potential source of preharvest pathogen contamination of vegetables. Hence, several organizations have recommended microbiological standards for water used to irrigate edible plants. The purpose of this study was to determine the strength of association between microbial quality indicators (coliforms and Escherichia coli) in irrigation water and on irrigated vegetables. Data analyzed included original results from a cross-sectional study conducted in the Midwestern United States during summer 2009 and information presented in two previously published studies performed in France and Portugal to investigate microbial quality of irrigation water and watered produce. In the cross-sectional study, repetitive PCR (rep-PCR) was used to characterize genetic relatedness of E. coli isolates from water and vegetables. No significant correlations were found between fecal indicators on leafy greens (lettuce and parsley, n = 91) or fruit (tomatoes and green peppers, n = 22) and those found in irrigation water used in the cross-sectional study (P > 0.40) or in the previously published data sets (data set 1: lettuce and waste irrigation water, n = 15, P > 0.40; data set 2: lettuce and irrigation water, n = 32, P = 0.06). Rep-PCR banding patterns of E. coli strains were all distinguishable among the pairs of E. coli isolates recovered from produce and irrigation water on the same farm. From the available data, the concentration of indicator organisms based on a single measure of irrigation water quality was not associated with the presence of these indicators on produce. In the absence of additional information, the use of a single microbial water quality parameter as an indicator of produce safety is of limited value for predicting the safety of the produce.

Choosing the most appropriate technique for wastewater disinfection – parallel investigation of four disinfection systems with different preceding treatment processes

A variety of bacterial, viral and parasitic pathogens are transmitted via water. Adequate disinfection of wastewater is therefore vital to address the potential health risks of water reuse. A range of well-established methods is available for wastewater disinfection. The selection of the most appropriate technology plays a key role in enhancing the safety, acceptability and reliability of water reuse systems. The objective of this study was the parallel examination of well-established and emerging wastewater disinfection methods, with particular attention being paid to the preceding wastewater treatment processes. The disinfectants investigated were: ultraviolet (UV) radiation, ozone (O3), chlorine dioxide (ClO2) and electrolytically-produced chlorine gas (Cl2). In order to support the specific selection of the most appropriate disinfection method, multiple criteria were determined: concentrations of indicator organisms, effluent toxicity, microbiological stability of the effluent, costs, energy consumption, and supplementary effects. The results show that stringent hygienic treatment objectives can be met with each of the applied methods immediately after disinfection, while the results of the evaluation of the further criteria differ widely between the analysed disinfectants.

Generic Modelling of Faecal Indicator Organism Concentrations in the UK

To meet European Water Framework Directive requirements, data are needed on faecal indicator organism (FIO) concentrations in rivers to enable the more heavily polluted to be targeted for remedial action. Due to the paucity of FIO data for the UK, especially under high-flow hydrograph event conditions, there is an urgent need by the policy community for generic models that can accurately predict FIO concentrations, thus informing integrated catchment management programmes. This paper reports the development of regression models to predict base- and high-flow faecal coliform (FC) and enterococci (EN) concentrations for 153 monitoring points across 14 UK catchments, using land cover, population (human and livestock density) and other variables that may affect FIO source strength, transport and die-off. Statistically significant models were developed for both FC and EN, with greater explained variance achieved in the high-flow models. Both land cover and, in particular, population variables are significant predictors of FIO concentrations, with r2 maxima for EN of 0.571 and 0.624, respectively. It is argued that the resulting models can be applied, with confidence, to other UK catchments, both to predict FIO concentrations in unmonitored watercourses and evaluate the likely impact of different land use/stocking level and human population change scenarios.

Predicting microbial pollution concentrations in UK rivers in response to land use change

The Water Framework Directive has caused a paradigm shift towards the integrated management of recreational water quality through the development of drainage basin-wide programmes of measures. This has increased the need for a cost-effective diagnostic tool capable of accurately predicting riverine faecal indicator organism (FIO) concentrations. This paper outlines the application of models developed to fulfil this need, which represent the first transferrable generic FIO models to be developed for the UK to incorporate direct measures of key FIO sources (namely human and livestock population data) as predictor variables. We apply a recently developed transfer methodology, which enables the quantification of geometric mean presumptive faecal coliforms and presumptive intestinal enterococci concentrations for base- and high-flow during the summer bathing season in unmonitored UK watercourses, to predict FIO concentrations in the Humber river basin district. Because the FIO models incorporate explanatory variables which allow the effects of policy measures which influence livestock stocking rates to be assessed, we carry out empirical analysis of the differential effects of seven land use management and policy instruments (fiscal constraint, production constraint, cost intervention, area intervention, demand-side constraint, input constraint, and micro-level land use management) all of which can be used to reduce riverine FIO concentrations. This research provides insights into FIO source apportionment, explores a selection of pollution remediation strategies and the spatial differentiation of land use policies which could be implemented to deliver river quality improvements. All of the policy tools we model reduce FIO concentrations in rivers but our research suggests that the installation of streamside fencing in intensive milk producing areas may be the single most effective land management strategy to reduce riverine microbial pollution.

Evaluating short-term changes in recreational water quality during a hydrograph event using a combination of microbial tracers, environmental microbiology, microbial source tracking and hydrological techniques: A case study in Southwest Wales, UK

Quantitative assessment of multiple sources to short-term variations in recreational water quality, as indexed by faecal indicator organism (FIO) concentrations, is becoming increasingly important with adoption of modern water quality standards and catchment-based water quality management requirements (e.g. the EU Water Framework Directive, Article 11 ‘ Programmes of Measures’ and the US Clean Water Act, ‘ Total Maximum Daily Loads’). This paper describes a study combining microbial tracers, intensive FIO measurement, open channel hydrology and molecular microbial source tracking (MST) to enhance understanding of recreational water quality at Amroth in southwest Wales, UK. Microbial tracers were released from four stream inputs during a moderate hydrograph event. Tracers from two local streams impacted simultaneously with a period of maximum FIO concentrations at the near-shore compliance monitoring site. Connection between these inputs and this site were rapid (9–33 min). Water quality impairment from a more remote stream input followed, 12.85 h after tracer release, sustaining FIO concentrations above desired compliance levels. MST analysis showed dominance of ruminant Bacteroidales genetic markers, associated with agricultural pollution. This integration of tracers and MST offers additional information on the movement and individual sources causing water quality impairment.

Microbial risks associated with exposure to pathogens in contaminated urban flood water

Urban flood incidents induced by heavy rainfall in many cases entail flooding of combined sewer systems. These flood waters are likely to be contaminated and may pose potential health risks to citizens exposed to pathogens in these waters. The purpose of this study was to evaluate the microbial risk associated with sewer flooding incidents. Concentrations of Escherichia coli, intestinal enterococci and Campylobacter were measured in samples from 3 sewer flooding incidents. The results indicate faecal contamination: faecal indicator organism concentrations were similar to those found in crude sewage under high-flow conditions and Campylobacter was detected in all samples. Due to infrequent occurrence of such incidents only a small number of samples could be collected; additional data were collected from controlled flooding experiments and analyses of samples from combined sewers. The results were used for a screening-level quantitative microbial risk assessment (QMRA). Calculated annual risks values vary from 5 × 10 −6 for Cryptosporidium assuming a low exposure scenario to 0.03 for Giardia assuming a high exposure scenario. The results of this screening-level risk assessment justify further research and data collection to allow more reliable quantitative assessment of health risks related to contaminated urban flood waters.

Reducing the health risk by using rapid quantification methods for the monitoring of E. coli and Enterococci in bathing waters

Recreational waters are monitored worldwide to protect bathers from infectious diseases caused by waterborne pathogens associated with the pollution of natural recreational waters by human and animal feces. Water quality standards are typically based on measurements of the concentrations of fecal indicator organisms (Escherichia coli and Enterococcus) and are becoming more stringent. A complicating factor is the time required (18-36 hours) for completion of conventional culture-based methods (as approved by the US EPA or ISO institutions). During the lag time between sample collection and availability of results indicator and pathogen levels, weather and water conditions may change and thus related health risk may also change. By using new rapid analytical tools, critical control points can be monitored to provide information so that management actions can have an impact on the exposure risk. The aim of this study was to evaluate the capacity of two new alternative methods for the rapid and routine enumeration of E. coli and Enterococci in bathing waters: fluorimetric assays based on the measurement of enzymatic activities, and quantitative RT-PCR. Both methods are fast (1 hour for 6 samples analysed by one fluorescence spectrophotometer; 3 hours for the simultaneous analysis of 15 to 96 samples by RT-PCR) and their results (for the microbiological criteria of current European regulations) compared with those from the standard methods are congruent in more than 81% of analysed samples. Because these methods provide a faster assessment of water quality, they have the potential to significantly reduce health risk resulting from exposure to recreational waters and also reduce errors in beach closing.

Contact With Beach Sand Among Beachgoers and Risk of Illness

Recent studies of beach sand fecal contamination have triggered interest among scientists and in the media. Although evidence shows that beach sand can harbor high concentrations of fecal indicator organisms, as well as fecal pathogens, illness risk associated with beach sand contact is not well understood. Beach visitors at 7 US beaches were enrolled in the National Epidemiological and Environmental Assessment of Recreational Water (NEEAR) Study during 2003-2005 and 2007 and asked about sand contact on the day of their visit to the beach (digging in the sand, body buried in the sand). Then, 10-12 days after their visit, participants were telephoned to answer questions about any health symptoms experienced since the visit. The authors completed 27,365 interviews. Digging in the sand was positively associated with gastrointestinal illness (adjusted incidence proportion ratio (aIPR) = 1.13, 95% confidence interval (CI): 1.02, 1.25) and diarrhea (aIPR = 1.20, 95% CI: 1.05, 1.36). The association was stronger between those buried in the sand and gastrointestinal illness (aIPR = 1.23, 95% CI: 1.05, 1.43) and diarrhea (aIPR = 1.24, 95% CI: 1.01, 1.52). Nonenteric illnesses did not show a consistent association with sand contact activities. Sand contact activities were associated with enteric illness at beach sites. Variation in beach-specific results suggests that site-specific factors may be important in the risk of illness following sand exposure.

Fecal Contamination of Groundwater in a Small Rural Dryland Watershed in Central Chile

Research on microbiological groundwater quality was conducted in Chile in a rural watershed that has almost no other water source. Forty-two wells were randomly selected and levels of indicator bacteria - total coliforms (TC), fecal coliforms (FC), and fecal streptococci (FS) - were repeatedly measured during the four seasons of 2005. The aim of this study was to characterize microbiological groundwater quality, relate indicator levels to certain watershed features and management characteristics which are likely to affect water quality. The dynamics of seasonal temporal contamination was determined with statistical analyses of indicator organism concentrations. Nonparametric tests were used to analyze relationships between bacterial indicators in well water and other variables. TC, FC, and FS were found in all samples indicating the wells had been contaminated with human and animal fecal material. The frequency distribution of microorganisms fitted a logistic distribution. The concentrations appeared to be temporal and levels varied between seasons with higher concentrations in winter. The cause of contamination could be linked to the easy access of domestic animals to the wells and to the permeable well casing material. Local precipitation runoff directly influenced the bacterial concentrations found in the wells.

Analysis of seawater microbiological quality data in Greece from 1997 to 2006: association of risk factors with bacterial indicators

This study deals with the examination of quality of seawater bathing areas in Greece over a 10-year period and identifies risk factors for high bacteria indicator organism concentrations. Qualitative descriptive analysis was applied and the microbiological test results of 231,205 water samples were associated with pollution markers and other parameters. Measurements of Escherichia coli (99.6%) and enterococci (100%) were found to be in accordance with the mandatory value guidelines set by the new European Directive. An increasing trend for the yearly mean value of faecal streptococci was noted. Using logistic regression analysis, phenolic smell (OR = 2.10, CI = 2.04-2.16), rainfall the day before sampling (OR = 1.67, CI = 1.64-1.74), high seas (OR = 1.42, CI = 1.39-1.46) and rainfall on the day of sampling (OR = 1.27, CI = 1.20-1.33) were positively independently associated with high levels of bacterial indicators (total coliforms, faecal coliforms, faecal streptococci and E. coli). The highest risk, absolute risk value 42.8% (RR = 3.17, CI = 2.97-3.38), was measured when previous day rainfall, phenolic smell and high seas were simultaneously recorded. Such parameters should be further investigated as predetermining factors for the assessment of beach bathing water quality, providing a timely indication of water risk assessment.

Effects of Etiological Agent and Bather Shedding of Pathogens on Interpretation of Epidemiological Data Used to Establish Recreational Water Quality Standards

The overall goal of the study reported herein was to use techniques in the field of risk assessment (specifically a state-space population dynamic model of disease transmission within recreational waters) to explore the relative significance of (1) active shedding of microorganisms from bathers themselves, and (2) the type and concentration of etiological agent on the observed heterogeneity of the incidence of illness in epidemiological studies that have been used to develop ambient water quality criteria. The etiological agent and corresponding dose ingested during recreational contact was found to significantly impact the observed incidence of illness in an epidemiological study conducted in recreational water. In addition, the observed incidence of illness was found not to necessarily reflect background concentrations of indicator organisms, but rather microorganisms shed during recreational contact. Future revisions to ambient water quality criteria should address the etiological agent, dose, and the significance of microbial shedding relative to background concentrations of pathogens and indicator organisms in addition to the incidence of illness and concentration of indicator organisms. Without a quantitative assessment of these additional variables, study findings may potentially be site specific and not representative of the health risks associated with specific indicator concentrations in all recreational waters.

Artificial Intelligence-Based Inductive Models for Prediction and Classification of Fecal Coliform in Surface Waters

This paper describes the use of inductive models developed using two artificial intelligence (AI)-based techniques for fecal coliform prediction and classification in surface waters. The two AI techniques used include artificial neural networks (ANNs) and a fixed functional set genetic algorithm (FFSGA) approach for function approximation. While ANNs have previously been used successfully for modeling water quality constituents, FFSGA is a relatively new technique of inductive model development. This paper will evaluate the efficacy of this technique for modeling indicator organism concentrations. In scenarios where process-based models cannot be developed and/or are not feasible, efficient and effective inductive models may be more suitable to provide quick and reasonably accurate predictions of indicator organism concentrations and associated water quality violations. The relative performance of AI-based inductive models is compared with conventional regression models. When raw data are used in the development of the inductive models described in this paper, the AI models slightly outperform the traditional regression models. However, when log transformed data are used, all inductive models show comparable performance. While the work validates the strength of simple regression models, it also validated FFSGA to be an effective technique that competes well with other state-of-the-art and complex techniques such as ANNs. FFSGA comes with the added advantage of resulting in a simple, easy to use, and compact functional form of the model sought. This work adds to the limited amount of research on the use of data-driven modeling methods for indicator organisms.

Faecal indicator organism concentrations and catchment export coefficients in the UK

Characterisation of faecal indicator organism (FIO) concentrations and export coefficients for catchments with particular combinations of land use and under specific climatic regimes is critical in developing models to predict daily loads and apportion sources of the microbial parameters used to regulate water quality. Accordingly, this paper presents a synthesis of FIO concentration and export coefficient data for the summer bathing season, with some comparative winter data, for 205 river/stream sampling points widely distributed across mainland UK. In terms of both geometric mean (GM) FIO concentrations and export coefficients (expressed as cfukm−2h−1), the results reveal (1) statistically significant elevations at high flow compared with base flow, with concentrations typically increasing by more than an order of magnitude and export coefficients by about two orders; (2) significantly higher values in summer than in winter under high-flow conditions; and (3) extremely wide variability between the catchments (e.g. four orders of magnitude range for GM faecal coliform concentrations), which closely reflects land use—with urban areas and improved pastures identified as key FIO sources. Generally, these two most polluting land uses are concentrated in lowland areas where runoff (m3km−2h−1) is low compared with upland areas, which in the UK are dominated by rough grazing and forestry. Consequently, contrasts in export coefficients between land use types are less than for FIO concentrations. The GMs reported for most land use categories are based on ⩾13 sites and exhibit quite narrow confidence intervals. They may therefore be applied with some confidence to other catchments in the UK and similar geographical regions elsewhere. Examples are presented to illustrate how the results can be used to estimate daily summer base- and high-flow FIO loads for catchments with different land use types, and to assess the likely effectiveness of certain strategies for reducing FIO pollutant loadings in areas with extensive areas of lowland improved pasture.

Faecal indicator organism concentrations in sewage and treated effluents

The importance of faecal indicator organism (FIO) fluxes within drainage basins is increasing as the European Union (EU) Water Framework Directive and the United States Clean Water Act place requirements on regulators to manage point and diffuse sources of microbial pollution causing non-compliance (EU) or impairment (US) of receiving waters. Central to this management task is knowledge of the likely FIO concentrations in raw sewage and treated effluents, but few empirical data have been published in the peer-reviewed literature. Accordingly, this paper presents results for 1933 samples from 162 different sewage discharge sites in the UK and Jersey, which encompass 12 types of sewage-related discharge, representative of untreated sewage and primary-, secondary- and tertiary-treated effluents. Geometric means (GMs) and 95% confidence intervals (CIs) have been used to characterise base- and high-flow FIO concentrations. The data sets and sub-sets are mostly quite large ( n⩾40) and may therefore be applied with some confidence to comparable discharge sites in similar geographical regions. Very marked, statistically significant reductions in GM FIO concentrations result from secondary and tertiary treatment, and there are statistically significant differences between some secondary and some tertiary treatments. Flow conditions are also shown to be important: untreated sewage and effluent from primary treatment plant have lower concentrations at high flow, due to dilution within combined sewerage systems, whereas some treated effluents (e.g. from activated sludge plant) have higher concentrations at high flow because of the shorter residence time within the plant. Under base-flow conditions, secondary treatments result in estimated GM FIO reductions of 95.22–99.29% (cf. primary-treated effluent). Corresponding figures for tertiary treatment plants (cf. secondary-treated effluent) are 93.24–96.59% for reedbed/grass plots and 99.71–99.92% for UV disinfection. Results suggest that secondary and tertiary treatment plants are less effective under high-flow conditions, but further high-flow sampling is required to confirm this.

Characterisation of Indicator Organisms and Pathogens in Domestic Greywater for Recycling

Greywater from baths, showers and washbasins was collected separately from all other domestic wastewater at a university block of flats with a dual reticulation system and analysed for a range of contaminants including indicator organisms and pathogens. Greywater flow and temperature were also monitored and a diurnal variation was observed. Physical and chemical water quality parameters were similar to previously published data, although measured COD and BOD levels appeared to be lower, possibly due to settlement or biodegradation in the storage tanks. Plate counts and indicator organism concentrations were consistently high suggesting a high level of human bacterial contamination necessitating biological treatment and disinfection if the water is to be used for recycling. However, these high levels of indicator organisms did not correlate to pathogen presence and should not be used as pathogen indicators in greywater. One positive count of Salmonella veltereden was observed as well as low levels of Giardia. Cryptosporidium, Escherichia coli O157:H7, enteroviruses and Legionella were not identified in any of the samples. The research also highlighted a number of problems with the complexity of this type of sampling programme, such as identifying the most likely time to isolate pathogens and analysing an 'unusual' water source.

Microbiological investigations for sanitary assessment of wastewater treated in constructed wetlands

Microbiological investigations into the occurrence and fate of pathogens in wastewater were carried out in a multi-annual measurement programme, using samples from three artificial wetlands equipped with pre-treatment systems (multi-chamber septic tanks, lagoons) and predominantly treating domestic wastewater. In this study, the concentrations of indicator organisms and pathogenic or potentially pathogenic microorganisms were determined in the various components or stages of the systems. The evaluation of data from some 3.600 microbiological analyses and a comparison with older data from a plant which has already been operation for 18 y made it possible for the first time ever to include operational factors in the assessment. Average removal of all major indicator organisms and pathogens is 1.5-2.5 log units for one-stage systems and increases to 3-5 log units for multi-stage systems. Significant differences between horizontal and vertical filters were not found. If no clogging problems arise during their operation, multi-stage systems can meet the requirements of the EU bathing water and irrigation water directives. Influent concentration, wastewater temperature, and hydraulic loading rate were found to be major factors of influence. The performance of constructed wetlands in removing microorganisms is clearly superior to that of conventional biological activated sludge systems.

Predicting faecal indicator fluxes using digital land use data in the UK's sentinel Water Framework Directive catchment: The Ribble study

The Ribble drainage basin is the single UK sentinel study area chosen for examining the implementation of the EU Water Framework Directive (WFD 20/60/EC). The study which has generated the data for this paper was initiated to quantify ‘catchment-derived’ fluxes of faecal indicators originating from both point and diffuse sources to inform the competent authorities on the potential for, and prioritization of, further options for reducing the faecal indicator loadings to this crucial coastal environment. It represents the first UK drainage basin-scale ‘profile’ of faecal indicator sources as recommended by WHO [1999. Health Based Monitoring of Recreational Waters: The Feasibility of a New Approach; the “Annapolis Protocol”. World Health Organisation Geneva, Switzerland; 2003. Guidelines for Safe Recreational-Water Environments Volume 1: Coastal and Fresh-Waters. World Health Organisation Geneva, Switzerland] and incorporated into current drafts of the revised Bathing Water Directive [ Anon, 2004. Council of the European Communities Amended proposal for a Directive of the European Parliament and of the Council concerning the management of bathing water quality. Brussels 23rd June]. This paper focuses on the relationships between land use and faecal indicator organism concentrations in surface waters within this very large drainage basin (1583 km 2) containing some extensive urban areas. A geographical information system comprising readily available digital elevation, remotely sensed land cover and digital map data was used to generate the land use variables for subcatchments draining to 41 locations across the study area. Presumptive concentrations of coliforms, Escherichia coli and enterococci (colony forming unit (cfu) 100 ml −1) were measured at each location on at least 20 occasions over a 44-day period within the 2002 bathing season. The sampling programme targeted hydrograph events. Hydrometric records were used to allocate results as either base flow or high flow. At each site, geometric mean faecal indicator organism concentrations were significantly elevated at high flow compared to base flow. Stepwise regression modelling produced statistically significant models predicting geometric mean base and high-flow faecal indicator organism concentrations from land use variables ( r 2 : 49.5–68.1%). The dominant predictor variable in each case was the proportion of built-up land in subcatchments, suggesting that this land use type, with associated sewage-related inputs, is a critical source of faecal indicator organisms in this drainage basin.