Recent Papers on Microbial Toxins

Content Table

Energy forest irrigated with wastewater: a comparative microbial risk assessment

Journal of Water and Health Vol 07 No 3 pp 413–433 © IWA Publishing 2009 doi:10.2166/wh.2009.020

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A. Carlander, C. Schönning and T. A. Stenström

Swedish Institute for Infectious Disease Control, SE-171 82 Solna, Sweden Tel.: +46 8 457 24 61 Fax: +46 8 32 83 30 E-mail: anneli.carlander@smi.se
 Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden
 Stockholm Environment Institute, SE-10691 Stockholm, Sweden; And Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences, N-1432 Aas, Norway

Abstract

In this study, risks for human infection associated with irrigation of municipal wastewater on short rotation willow coppice (Salix) were evaluated in three countries. The aim was also to determine the reduction of indicator organisms and pathogens in the treatment plants. Two of the field sites were chosen for further evaluation by QMRA (quantitative microbial risk assessment) applied to three scenarios: accidental ingestions of wastewater, exposure to aerosols and ingestion of groundwater. The risks of infection for bacteria (Salmonella), virus (rotavirus) and protozoa (Giardia, Cryptosporidium) were characterised as probability of infections per exposure and number of infections per year.

The highest risk for infection was associated with exposure to rotavirus in Culmore (Northern Ireland), by either accidental ingestion of wastewater or ingestion of groundwater (Pinf 8 × 10-1). For Kvidinge (Sweden) the risk for virus infection by ingestion of wastewater were in the same range (Pinf 7 × 10-1). The risk for Giardia infection differed between the two sites due to differences in concentration of this pathogen in the wastewater. The groundwater was found to have suffered faecal contamination due to the wastewater irrigation. Use of partially treated wastewater for irrigation of energy crops could be a sustainable option if site-specific recommendations are developed.

An approach for developing quantitative risk-based microbial standards for fresh produce

Journal of Water and Health Vol 6 No 3 pp 359–364 © IWA Publishing 2008 doi:10.2166/wh.2008.047

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Kristina D. Mena and Suresh D. Pillai

University of Texas Health Science Center at Houston, School of Public Health, P.O. Box 20186, Houston, TX 77225, USA
 Poultry Science & Nutrition and Food Science Departments, Texas A&M University 418D, Kleberg Center, MS 2472 Texas A&M University College Station, Texas, 77843-2472, USA Tel.: (979) 845-2994 Fax: (979) 845-1921 spillai@poultry.tamu.edu

Abstract

A key objective of the Good Agricultural Practices (GAP) program is to reduce the potential for produce to become contaminated with microbial pathogens, such as through irrigation water. Without microbial standards, however, it is impractical to decide whether there is a need to disinfect, a need to institute watershed protection programs, or a need to institute post-harvest disinfection regimes. To develop such standards, quantitative microbial risk assessments can be performed using pathogen monitoring data for produce. This paper presents an approach which can be used towards the application of a risk assessment framework to developing microbial standards for fresh produce. Risks of infection are estimated using typical monitoring data of Salmonella detected on carrots and assuming various scenarios of the likelihood of an individual consuming a contaminated serving of carrots in a given year. Estimated annual risks of infection range from 2.20 × 10-5 to 2.16 × 10-3, assuming 1% and 100% of an individual's carrot servings are contaminated, respectively. In addition, critical factors are identified which need to be incorporated in such a risk assessment approach as well as their impact on risk estimates to provide growers with benchmarks which may be targeted to reduce health risks.

Improved methods for modelling drinking water treatment in quantitative microbial risk assessment; a case study of Campylobacter reduction by filtration and ozonation

Journal of Water and Health Vol 6 No 3 pp 301–314 © IWA Publishing 2008 doi:10.2166/wh.2008.066

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P. W. M. H. Smeets, G. J. Medema, Y. J. Dullemont, P. H. A. J. M. Van Gelder and J. C. Van Dijk

Kiwa Water Research, PO BOX 1072, 3430 BB, Nieuwegein, The Netherlands Tel.: +31 30 6069511 E-mail: patrick.smeets@kiwa.nl
 Waternet, PO Box 8169, Amsterdam, 1005 AD, The Netherlands
 Delft University of Technology, PO BOX 5048, 2600 GA, Delft, The Netherlands

Abstract

Quantitative microbial risk assessment (QMRA) is increasingly applied to estimate drinking water safety. In QMRA the risk of infection is calculated from pathogen concentrations in drinking water, water consumption and dose response relations. Pathogen concentrations in drinking water are generally low and monitoring provides little information for QMRA. Therefore pathogen concentrations are monitored in the raw water and reduction of pathogens by treatment is modelled stochastically with Monte Carlo simulations. The method was tested in a case study with Campylobacter monitoring data of rapid sand filtration and ozonation processes. This study showed that the currently applied method did not predict the monitoring data used for validation. Consequently the risk of infection was over estimated by one order of magnitude. An improved method for model validation was developed. It combines non-parametric bootstrapping with statistical extrapolation to rare events. Evaluation of the treatment model was improved by presenting monitoring data and modelling results in CCDF graphs, which focus on the occurrence of rare events. Apart from calculating the yearly average risk of infection, the model results were presented in FN curves. This allowed for evaluation of both the distribution of risk and the uncertainty associated with the assessment.

Long-term study of Cryptosporidium and Giardia occurrence and quantitative microbial risk assessment in surface waters of Arizona in the USA

Journal of Water and Health Vol 06 No 2 pp 263–273 © IWA Publishing 2008 doi:10.2166/wh.2008.030

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Hodon Ryu and Morteza Abbaszadegan

Abstract

A four-year systematic study of microbial water quality in the surface waters of central Arizona was performed. The objectives of this study were to investigate the occurrence of microbial pathogens and indicators in the waters. A total of 192 water samples from five sites were analyzed for Cryptosporidium, Giardia, and various microbial and physical indicators. Ten percent (16/162) of the samples collected using EnviroChek filters were positive for Cryptosporidium oocysts, whereas no oocysts (<1 in 5 L) were detected in the grab samples (0/30). Giardia cysts were detected in 10% (3/30) of the grab samples and in 27% (44/162) samples collected using EnviroChek filters. Mean concentrations of oocysts in the source waters at the treatment plants were lower than the Bin 1 category of the USEPA Long Term 2 Enhanced Surface Water Treatment Rule; therefore no additional treatment is required by the plants. The annual risks of infection from Cryptosporidium met the annual acceptable risk of 10-4 at all sampling sites, whereas the risks of Giardia infection at the Verde River and the Salt River were 5.70E-04 and 2.66E-04, respectively.

Legionnaires' disease: evaluation of a quantitative microbial risk assessment model

Journal of Water and Health Vol 06 No 2 pp 149–166 © IWA Publishing 2008 doi:10.2166/wh.2008.026

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Thomas W. Armstrong and Charles N. Haas

Abstract

Background: The quantities of Legionella vary considerably from natural waters to water in contaminated domestic hot water supplies, whirlpool spas and cooling towers, with the risk for LD rising as the Legionella counts grow. We currently report the results from our Quantitative Microbial Risk Assessment (QMRA) model evaluation. We developed the LD QMRA model to better understand Legionella exposure risks.

Methods: Using an animal data derived model for LD, we calculated risks from estimated exposures for a whirlpool spa outbreak, two hot spring spa outbreaks and compared the results to the reported LD risks.

Results: The QMRA model shows agreement (generally less than an order of magnitude discrepancy) with the reported Legionnaires' disease sub-clinical severity infection, clinical severity infection, and mortality risks.

Conclusions: The LD QMRA model may lead to risk based limits to supplement the current guidance on Legionella control in cooling towers, whirlpool spas and other potential exposure sources. The verification of QMRA for LD also suggests the techniques, given suitable animal model data, may be useful in quantifying human response to other airborne pathogens.

Microbial risk assessment of local handling and use of human faeces

Journal of Water and Health Vol 5 No 1 pp 117–128 © IWA Publishing 2007 doi:10.2166/wh.2006.049

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Caroline Schönning, Therese Westrell, Thor Axel Stenström, Karsten Arnbjerg-Nielsen, Arne Bernt Hasling, Linda Høibye and Anders Carlsen

Department of Mycology, Parasitology and Environmental Microbiology, Swedish Institute for Infectious Disease Control, SE-171 82Solna, Sweden
 COWI A/S, DK-2800, Lyngby, Denmark Ph.: +45 4597 1367 kar@cowi.dk
 Embedslægeinstitutionen, DK-8800, Viborg, Denmark

Abstract

Dry urine-diverting toilets may be used in order to collect excreta for the utilisation of nutrients. A quantitative microbial risk assessment was conducted in order to evaluate the risks of transmission of infectious disease related to the local use of faeces as a fertiliser. The human exposures evaluated included accidental ingestion of small amounts of faeces, or a mixture of faeces and soil, while emptying the storage container and applying the material in the garden, during recreational stays to the garden, and during gardening. A range of pathogens representing various groups of microorganisms was considered. Results showed that 12-months' storage before use was sufficient for the inactivation of most pathogens to acceptable levels. When working or spending time in the garden the annual risk of infection by Ascaris was still slightly above 10-4 in these scenarios, although the incidence rate for Ascaris is very low in the population in question. Measures to further reduce the hygienic risks include longer storage, or treatment, of the faeces. The results can easily be extended to other regions with different incidence rates.

Identification and management of microbial contaminations in a surface drinking water Source

Journal of Water and Health Vol 5 No Suppl 1 pp S67–S79 © IWA Publishing 2007 doi:10.2166/wh.2007.137ce

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J. Åström, T. J. R. Pettersson and T. A. Stenström

Department of Civil and Environmental Engineering, Water Environment Technology, Chalmers University of Technology, SE-412 96, Göteborg, Sweden Tel.: +46 31 7722154; Fax: +46 31 7725695; johan.l.astrom@chalmers.se
 Department of Parasitology, Mycology, Water and Environmental Microbiology, Swedish Institute for Infectious Disease Control, SE-171 82, Solna, Sweden

Abstract

Microbial contamination of surface waters constitutes a health risk for drinking water consumers which may be lowered by closing the raw water intake. We have evaluated microbial discharge events reported in the river Göta älv, which is used for raw water supply to the city of Göteborg. Elevated levels of faecal indicator bacteria were observed during periods of closed raw water intake. High bacteria levels were, however, also occasionally detected during periods of open intake, probably as a result of microbial discharge far upstream in the river which may be difficult to predict and manage by closing the intake. Accumulated upstream precipitations, resulting in surface runoff and wastewater contaminations in the catchment, correlated positively with the levels of total coliforms, E. coli, intestinal enterococci and sulfite-reducing clostridia. Levels of faecal indicator organisms were negatively correlated to the water temperature due to enhanced survival at lower temperatures. Wastewater discharges from a municipality located just upstream of the water intake resulted in elevated E. coli concentrations downstream at the raw water intake for Göteborg. To improve the prediction of microbial contaminations within the river Göta älv, monitoring data on turbidity and upstream precipitation are of particular importance.

Evaluation of the microbial risk reduction due to selective closure of the raw water intake before drinking water treatment

Journal of Water and Health Vol 5 No Suppl 1 pp S81–S97 © IWA Publishing 2007 doi:10.2166/wh.2007.139

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J. Åström, S. Petterson, O. Bergstedt, T. J. R. Pettersson and T. A. Stenström

Department of Civil and Environmental Engineering, Water Environment Technology, Chalmers University of Technology, SE-412 96, Göteborg, Sweden Tel.: +46 31 772 2154 Fax: +46 31 772 5695 johan.l.astrom@chalmers.se
 Centre for Water and Waste Technology, School of Civil and Environmental Engineering, University of New South Wales, UNSW, -, Sydney, NSW 2052, Australia
 Göteborg Water, City of Göteborg, Box 123, SE-424 23, Angered, Sweden
 Department of Parasitology, Mycology, Water and Environmental Microbiology, Swedish Institute for Infectious Disease Control, SE-171 82, Solna, Sweden

Abstract

Short-term peaks in pathogen concentrations may increase the risks for waterborne diseases considerably. In this study the occurrence of indicator organisms and pathogens in the river Göta älv at the raw water intake to Göteborg was evaluated and related to risk for drinking water consumption. About half of the 24 pathogen samples, taken during event and non-event conditions, were positive for at least one of the following: Cryptosporidium, Giardia, norovirus, enterovirus, Campylobacter and E. coli O157. Positive pathogen detects were often associated with heavy rainfalls and viruses with a sewage emergency discharge. The annualised probability of infection from this type of event was calculated from pathogen concentrations in a QMRA model. Given that the water intake is not closed, the risk given present water treatment seems to be acceptable for Giardia; however, it is at a borderline for Cryptosporidium and insufficient for noro- and enteroviruses. Present results emphasise the need for an appropriate intake regulation with respect to high pathogen loads, as the risk increases with time of exposure to pathogen contaminants. Rather than a threshold level on E. coli, reports on upstream microbial discharges are valuable for quick pathogen indications.

An assessment of water quality and microbial risk in Rio Grande basin in the United States-Mexican border region

J Water Health 03 (2005) 209-218

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Hodon Ryu, Absar Alum, Morteza Abbaszadegan, Maria Alvarez and Jose Mendoza

National Science Foundation Water Quality Center, Department of Civil and Environmental Engineering, Arizona State University, PO Box 875306, Tempe, AZ, 85281-5306, USA, Tel: 480-965-3868, Fax: 480-965-0557, E-mail: abbaszadegan@asu.edu

National Science Foundation Water Quality Center, Department of Civil and Environmental Engineering, Arizona State University, PO Box 875306, Tempe, AZ, 85281-5306, USA, Tel: 480-965-3868, Fax: 480-965-0557, E-mail: abbaszadegan@asu.edu

National Science Foundation Water Quality Center, Department of Civil and Environmental Engineering, Arizona State University, PO Box 875306, Tempe, AZ, 85281-5306, USA, Tel: 480-965-3868, Fax: 480-965-0557, E-mail: abbaszadegan@asu.edu

Department of Biology, El Paso Community College, PO Box 20500, El Paso, TX, 79998, USA

National Science Foundation Water Quality Center, Department of Civil and Environmental Engineering, Arizona State University, PO Box 875306, Tempe, AZ, 85281-5306, USA, Tel: 480-965-3868, Fax: 480-965-0557, E-mail: abbaszadegan@asu.edu

Abstract

Increased reliance of urban populations on Rio Grande water has necessitated an expanded microbial surveillance of the river to help identify and evaluate sources of human pathogens, which could pose a public health risk. The objectives of this study were to investigate microbial and chemical water quality in Rio Grande water and to perform risk assessment analyses for Cryptosporidium. No oocysts in any of the ten-litre samples were detected. However, the limit of detection in the water samples ranged between 20 and 200 oocysts/100 L. The limits of detection obtained in this study would result in one to two orders of magnitude higher risk of infection for Cryptosporidium than the U.S.EPA annual acceptable risk level of 10-4. The bacterial data showed the significance of animal farming and raw sewage as sources of fecal pollution. Male specific and somatic coliphages were detected in 52% (11/21) and 62% (24/39) of the samples, respectively. Somatic coliphages were greater by one order of magnitude, and were better correlated with total (r2=0.6801; p≤0.05) and fecal coliform bacteria (r2=0.7366; p≤0.05) than male specific coliphages. The dissolved organic carbon (DOC) and specific ultraviolet absorbance (SUVA) values ranged 2.58-5.59 mg/L and 1.23-2.29 m-1 (mg/l)-1, respectively. Low SUVA values of raw water condition make it difficult to remove DOC during physical and chemical treatment processes. The microbial and chemical data provided from this study can help drinking water utilities to maintain balance between greater microbial inactivation and reduced disinfection by-products (DBPs) formation.

Development of a toolbox to assess microbial contamination risks in small water systems

J Water Health 02 (2004) 217-232

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Phillip W. Butterfield and Anne K. Camper

University of Washington, Department of Environmental and Occupational Health Sciences, 4225 Roosevelt Way NE, Suite 100, Seattle, WA 98105, USA Tel: (206) 616-4213 Fax: (206) 543-8123 E-mail: pbutter2@u.washington.edu

Center for Biofilm Engineering, Montana State University, 366 EPS Building, Bozeman, MT 59717, USA

Abstract

Individual and small water systems account for the majority of waterborne disease outbreaks recorded in the United States each year. To address this problem a project was undertaken to develop a comprehensive self-assessment toolbox that could be used by small water system personnel to determine where their system has the greatest potential risks from microbial contamination. The toolbox components consist of: (1) a survey that asks specific questions; (2) a ranking tool that computes numerical scores for water system components based on survey answers; (3) comments and results from the ranking tool; (4) a guidance document to help the user understand why certain conditions may represent a risk; and (5) instructions for using the toolbox. A unique feature of the ranking tool is the ability to input expert opinion in the form of scores for each answer and weighting factors. Weighting factors are derived using ranked, pairwise comparisons, and then used to determine numerical scores for system components. Toolbox administrators are allowed to modify weighting factors used by the ranking tool application, thus allowing input of expert opinion.

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