Comparing probabilistic microbial risk assessments for drinking water against daily rather than annualised infection probability targets

Abstract

Some national drinking water guidelines provide guidance on how to define 'safe' drinking water.Regarding microbial water quality, a common position is that the chance of an individual becoming infected by some reference waterborne pathogen (e.g. Cryptsporidium) present in the drinking water should ,10 24 in any year. However the instantaneous levels of risk to a water consumer vary over the course of a year, and waterborne disease outbreaks have been associated with shorter-duration periods of heightened risk. Performing probabilistic microbial risk assessments is becoming commonplace to capture the impacts of temporal variability on overall infection risk levels. A case is presented here for adoption of a shorter-duration reference period (i.e. daily) infection probability target over which to assess, report and benchmark such risks. A daily infection probability benchmark may provide added incentive and guidance for exercising control over short-term adverse risk fluctuation events and their causes. Management planning could involve outlining measures so that the daily target is met under a variety of pre-identified event scenarios. Other benefits of a daily target could include providing a platform for managers to design and assess management initiatives, as well as simplifying the technical components of the risk assessment process.

Comparison of Risk Predicted by Multiple Norovirus Dose–Response Models and Implications for Quantitative Microbial Risk Assessment

“…The results were also compared against the annual risk of infection guideline for drinking water of less than 1 infection per 10,000 individuals per year, (76,77) which would yield an allowable daily risk of approximately 1 in 1,000,000. (78) The results from Table IV indicate that for a dose of <100 gec (4 of 19 doses), the highest predicted probability of infection values were estimated by FPx_PGIa+bGII followed by 1F1x_TGIa+b. At very low doses (<1 gec), all dose-response models predicted probability of infection values near 0.001 except FPx_PGIa+bGII and 1F1x_TGIa+b, which predicted 0.38 and 0.22, respectively, at a dose of 0.736 gec.…”

“…The assumption was made that if a person was infected he or she became ill. The results were also compared against the annual risk of infection guideline for drinking water of less than 1 infection per 10,000 individuals per year, which would yield an allowable daily risk of approximately 1 in 1,000,000 …”

Patógenos e indicadores microbiológicos de calidad del agua para consumo humano

“…El agua es la sustancia más común e importante en la tierra y su disponibilidad ha sido el factor más crítico para la supervivencia durante el desarrollo de toda forma viva en el planeta [47]. En la historia de la humanidad los centros culturales y los asentamientos humanos siempre se fundaron en zonas con suministro suficiente de agua dulce y a medida que la población aumentaba el suministro natural de agua se iba limitando, por lo que las grandes culturas desarrollaron técnicas y sistemas sofisticados para lograr el acceso a nuevos depósitos de agua [p.e.…”

“…Pero muy pronto otras complicaciones de las zonas densamente pobladas, como la creciente cantidad de residuos, aguas residuales y otros tipos de contaminación, se convirtieron también en factores peligrosos sobre el agua potable [37]. Además de los problemas de higiene causados por los residuos insalubres el rápido desarrollo de la industria, especialmente el desarrollo de la industria química, ha dado lugar a una contaminación permanente de todos los tipos de sistemas de agua naturales, que no sólo se observa en los países altamente industrializados sino en todos los lugares del planeta; incluso se ha encontrado que la nieve y el hielo del Ártico y la Antártida, contienen contaminantes biológicos y químicos que se derivan principalmente de los países industrializados del hemisferio norte [47][48][49].…”

“…El cumplimiento de estos requisitos exige la protección de los recursos y el riguroso tratamiento del agua cruda, así como el control de calidad exhaustivo del proceso. Sin embargo, la evaluación del comportamiento de los agentes patógenos en el agua potable es también esencial como base para futuras mejoras en el proceso de tratamiento y la generación de nuevos reglamentos [21,47].…”