Application of Microbial Risk Assessment to the Development of Standards for Enteric Pathogens in Water Used To Irrigate Fresh Produce

2005 ◽  
Vol 68 (5) ◽  
pp. 913-918 ◽  
Author(s):  
SCOTT W. STINE ◽  
INHONG SONG ◽  
CHRISTOPHER Y. CHOI ◽  
CHARLES P. GERBA
Keyword(s):  
Risk Assessment ◽  
Irrigation Water ◽  
Fresh Produce ◽  
Enteric Bacteria ◽  
Irrigation Event ◽  
Risk Of Infection ◽  
Probable Number ◽  
Microbial Risk Assessment ◽  
Microbial Risk ◽  
Annual Risk

Microbial contamination of the surfaces of cantaloupe, iceberg lettuce, and bell peppers via contact with irrigation water was investigated to aid in the development of irrigation water quality standards for enteric bacteria and viruses. Furrow and subsurface drip irrigation methods were evaluated with the use of nonpathogenic surrogates, coliphage PRD1, and Escherichia coli ATCC 25922. The concentrations of hepatitis A virus (HAV) and Salmonella in irrigation water necessary to achieve a 1:10,000 annual risk of infection, the acceptable level of risk used for drinking water by the U.S. Environmental Protection Agency, were calculated with a quantitative microbial risk assessment approach. These calculations were based on the transfer of the selected nonpathogenic surrogates to fresh produce via irrigation water, as well as previously determined preharvest inactivation rates of pathogenic microorganisms on the surfaces of fresh produce. The risk of infection was found to be variable depending on type of crop, irrigation method, and days between last irrigation event and harvest. The worst-case scenario, in which produce is harvested and consumed the day after the last irrigation event and maximum exposure is assumed, indicated that concentrations of 2.5 CFU/100 ml of Salmonella and 2.5 × 10−5 most probable number per 100 ml of HAV in irrigation water would result in an annual risk of 1:10,000 when the crop was consumed. If 14 days elapsed before harvest, allowing for die-off of the pathogens, the concentrations were increased to 5.7 × 103 Salmonella per 100 ml and 9.9 × 10−3 HAV per 100 ml.

scholarly journals Microbial risk assessment of local handling and use of human faeces

2006 ◽  
Vol 5 (1) ◽  
pp. 117-128 ◽  
Author(s):  
Caroline Schönning ◽  
Therese Westrell ◽  
Thor Axel Stenström ◽  
Karsten Arnbjerg-Nielsen ◽  
Arne Bernt Hasling ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Incidence Rates ◽  
Quantitative Microbial Risk Assessment ◽  
Risk Of Infection ◽  
Accidental Ingestion ◽  
Storage Container ◽  
Microbial Risk Assessment ◽  
Microbial Risk ◽  
Local Use ◽  
Annual Risk

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.

scholarly journals Quantitative Microbial Risk Assessment Models for Consumption of Raw Vegetables Irrigated with Reclaimed Water

2006 ◽  
Vol 72 (5) ◽  
pp. 3284-3290 ◽  
Author(s):  
Andrew J. Hamilton ◽  
Frank Stagnitti ◽  
Robert Premier ◽  
Anne-Maree Boland ◽  
Glenn Hale
Keyword(s):  
Risk Assessment ◽  
Reclaimed Water ◽  
Quantitative Microbial Risk Assessment ◽  
Risk Of Infection ◽  
Worst Case ◽  
Microbial Risk Assessment ◽  
Microbial Risk ◽  
Risk Assessment Models ◽  
Crop Type ◽  
Annual Risk

ABSTRACT Quantitative microbial risk assessment models for estimating the annual risk of enteric virus infection associated with consuming raw vegetables that have been overhead irrigated with nondisinfected secondary treated reclaimed water were constructed. We ran models for several different scenarios of crop type, viral concentration in effluent, and time since last irrigation event. The mean annual risk of infection was always less for cucumber than for broccoli, cabbage, or lettuce. Across the various crops, effluent qualities, and viral decay rates considered, the annual risk of infection ranged from 10−3 to 10−1 when reclaimed-water irrigation ceased 1 day before harvest and from 10−9 to 10−3 when it ceased 2 weeks before harvest. Two previously published decay coefficients were used to describe the die-off of viruses in the environment. For all combinations of crop type and effluent quality, application of the more aggressive decay coefficient led to annual risks of infection that satisfied the commonly propounded benchmark of ≤10−4, i.e., one infection or less per 10,000 people per year, providing that 14 days had elapsed since irrigation with reclaimed water. Conversely, this benchmark was not attained for any combination of crop and water quality when this withholding period was 1 day. The lower decay rate conferred markedly less protection, with broccoli and cucumber being the only crops satisfying the 10−4 standard for all water qualities after a 14-day withholding period. Sensitivity analyses on the models revealed that in nearly all cases, variation in the amount of produce consumed had the most significant effect on the total uncertainty surrounding the estimate of annual infection risk. The models presented cover what would generally be considered to be worst-case scenarios: overhead irrigation and consumption of vegetables raw. Practices such as subsurface, furrow, or drip irrigation and postharvest washing/disinfection and food preparation could substantially lower risks and need to be considered in future models, particularly for developed nations where these extra risk reduction measures are more common.

scholarly journals Zero Risk Does Not Exist: Lessons Learned from Microbial Risk Assessment Related to Use of Water and Safety of Fresh Produce

2015 ◽  
Vol 14 (4) ◽  
pp. 387-410 ◽  
Author(s):  
Ann De Keuckelaere ◽  
Liesbeth Jacxsens ◽  
Philip Amoah ◽  
Gertjan Medema ◽  
Peter McClure ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Fresh Produce ◽  
Lessons Learned ◽  
Microbial Risk Assessment ◽  
Microbial Risk

scholarly journals Evaluation of Various Campylobacter-Specific Quantitative PCR (qPCR) Assays for Detection and Enumeration of Campylobacteraceae in Irrigation Water and Wastewater via a Miniaturized Most-Probable-Number–qPCR Assay

2016 ◽  
Vol 82 (15) ◽  
pp. 4743-4756 ◽  
Author(s):  
Graham S. Banting ◽  
Shannon Braithwaite ◽  
Candis Scott ◽  
Jinyong Kim ◽  
Byeonghwa Jeon ◽  
...  
Keyword(s):  
Irrigation Water ◽  
Water Samples ◽  
Qpcr Assay ◽  
Most Probable Number ◽  
Quantitative Microbial Risk Assessment ◽  
Detection Rates ◽  
Probable Number ◽  
Content Type ◽  
Microbial Risk Assessment ◽  
Microbial Risk

ABSTRACTCampylobacterspp. are the leading cause of bacterial gastroenteritis worldwide, and water is increasingly seen as a risk factor in transmission. Here we describe a most-probable-number (MPN)–quantitative PCR (qPCR) assay in which water samples are centrifuged and aliquoted into microtiter plates and the bacteria are enumerated by qPCR. We observed that commonly usedCampylobactermolecular assays produced vastly different detection rates. In irrigation water samples, detection rates varied depending upon the PCR assay and culture method used, as follows: 0% by the de Boer Lv1-16S qPCR assay, 2.5% by the Van Dyke 16S and JensenglyAqPCR assays, and 75% by the Linton 16S endpoint PCR when cultured at 37°C. Primer/probe specificity was the major confounder, withArcobacterspp. routinely yielding false-positive results. The primers and PCR conditions described by Van Dyke et al. (M. I. Van Dyke, V. K. Morton, N. L. McLellan, and P. M. Huck, J Appl Microbiol 109:1053–1066, 2010,http://dx.doi.org/10.1111/j.1365-2672.2010.04730.x) proved to be the most sensitive and specific forCampylobacterdetection in water.Campylobacteroccurrence in irrigation water was found to be very low (<2 MPN/300 ml) when thisCampylobacter-specific qPCR was used, with the most commonly detected species beingC. jejuni,C. coli, andC. lari. Campylobacters in raw sewage were present at ∼102/100 ml, with incubation at 42°C required for reducing microbial growth competition from arcobacters. Overall, whenCampylobacterprevalence and/or concentration in water is reported using molecular methods, considerable validation is recommended when adapting methods largely developed for clinical applications. Furthermore, combining MPN methods with molecular biology-based detection algorithms allows for the detection and quantification ofCampylobacterspp. in environmental samples and is potentially suited to quantitative microbial risk assessment for improved public health disease prevention related to food and water exposures.IMPORTANCEThe results of this study demonstrate the importance of assay validation upon data interpretation of environmental monitoring forCampylobacterwhen using molecular biology-based assays. Previous studies describingCampylobacterprevalence in Canada utilized primers that we have determined to be nonspecific due to their cross-amplification ofArcobacterspp. As such,Campylobacterprevalence may have been vastly overestimated in other studies. Additionally, the development of a quantitative assay described in this study will allow accurate determination ofCampylobacterconcentrations in environmental water samples, allowing more informed decisions to be made about water usage based on quantitative microbial risk assessment.

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

2008 ◽  
Vol 6 (3) ◽  
pp. 301-314 ◽  
Author(s):  
P. W. M. H. Smeets ◽  
Y. J. Dullemont ◽  
P. H. A. J. M. Van Gelder ◽  
J. C. Van Dijk ◽  
G. J. Medema
Keyword(s):  
Risk Assessment ◽  
Drinking Water ◽  
Rare Events ◽  
Monitoring Data ◽  
Average Risk ◽  
Quantitative Microbial Risk Assessment ◽  
Risk Of Infection ◽  
Microbial Risk Assessment ◽  
Microbial Risk

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.

scholarly journals Quantitative microbial risk assessment used to evaluate seasonal wastewater treatment limits: case study in Vacaville, CA

2017 ◽  
Vol 18 (3) ◽  
pp. 910-925 ◽  
Author(s):  
Edmund Seto ◽  
Adam W. Olivieri ◽  
Richard E. Danielson
Keyword(s):  
Risk Assessment ◽  
Wastewater Treatment ◽  
Treatment Plant ◽  
Enteric Viruses ◽  
Secondary Effluent ◽  
Quantitative Microbial Risk Assessment ◽  
Microbial Risk Assessment ◽  
Microbial Risk ◽  
Annual Risk ◽  
Receiving Water

Abstract A quantitative microbial risk assessment (QMRA) was conducted to support renewal of the City of Vacaville wastewater discharge permit and seasonal (summer) filtration requirements. Influent and final disinfected effluent from the city's wastewater treatment plant, as well as 11 receiving water stations, were monitored for indicator organisms (i.e. total and fecal coliforms, Escherichia coli, Enterococcus, male-specific bacteriophage (MS2), and the Bacteroidales) and several pathogens (i.e. Giardia cysts, Cryptosporidium oocysts, infectious Cryptosporidium, and Norovirus GI and GII). QMRA annualized risks of infection for selected pathogens enteric viruses, Giardia and Cryptosporidium. Estimated median annualized risk for recreational exposure in either disinfected secondary and/or filtered disinfected secondary effluent is on the order of 1.1 × 10−3 per person per year (pppy) for enteric viruses and would be roughly one order of magnitude lower if local receiving water dilution of the treatment plant effluent was taken into account. Estimated median annual risk for recreation exposure in disinfected secondary effluent is 1.8 × 10−3 pppy for Cryptosporidium and 1 log10 less with filtration during the summer months. The estimated median annual risk for landscape exposure (e.g. golfing) to secondary disinfected effluent is 7.6 × 10−7 pppy for enteric viruses. Estimated median annualized risk is 1.7 × 10−7 pppy for enteric viruses and 3.0 × 10−5 to 3.6 × 10−6 pppy for parasites for use of secondary disinfected effluent with irrigated agriculture. Estimated annualized risks for recreational exposure to the local receiving waters were approximately 10 to 1,000 times greater than direct recreational exposure to the final filtered and disinfected effluent. All risk estimates associated with exposure to final treated plant effluent (i.e. secondary filtered and disinfected) were close to or lower than the California level of acceptable annual risk of infection of 10−4 pppy for recreational exposure. Risk estimates provide further evidence to support the use of seasonal treatment limits requiring summer filtration for public health protection.

Quantification of Giardia and Cryptosporidium in surface water: a risk assessment and molecular characterization

2019 ◽  
Vol 19 (6) ◽  
pp. 1823-1830 ◽  
Author(s):  
M. O. Bataiero ◽  
R. S. Araujo ◽  
A. C. Nardocci ◽  
M. H. Matté ◽  
M. I. Z. Sato ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Positive Impact ◽  
18S Rrna Gene ◽  
Rrna Gene ◽  
Quantitative Microbial Risk Assessment ◽  
Protection Measures ◽  
Microbial Risk Assessment ◽  
Microbial Risk ◽  
Contaminated Drinking Water ◽  
Annual Risk

Abstract This study aimed to estimate the annual probability of Giardia and Cryptosporidium infection for a population supplied by contaminated drinking water sources. Parasites were quantified by the USEPA Method 1623.1/2012. Annual risk was estimated using the quantitative microbial risk assessment (QMRA) approach. Genotyping was performed using specific primers based on the 18S rRNA gene for Cryptosporidium and gdh gene for Giardia. Giardia was detected in 83.3% of the samples (&lt;0.1 to 8.6 cysts/L) and Cryptosporidium in 37.5% (&lt;0.1 to 2 oocysts/L). In general, annual risk values for Giardia were 1 log higher when compared with those obtained for Cryptosporidium. Giardia intestinalis A and B were present as well as C. hominis and C. parvum. The lack of protection measures for the water supply catchment point put the population's health at risk. The results provide data to support decision-makers to take actions to improve environmental quality resulting in a positive impact on consumers' health.

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