Quantitative Microbial Risk Assessment of a Drinking Water-Wastewater Cross-Connection Simulation

By Mena, Kristina D.; Mota, Linda C. et al. | Journal of Environmental Engineering and Science, September 2008 | Go to article overview

Quantitative Microbial Risk Assessment of a Drinking Water-Wastewater Cross-Connection Simulation


Mena, Kristina D., Mota, Linda C., Meckes, Mark C., Green, Christopher F., Hurd, William W., Gibbs, Shawn G., Journal of Environmental Engineering and Science


Abstract: Quantitative microbial risk assessment is a useful way to predict the incidence of infection and illness within a community following exposure to pathogens. We used this risk assessment technique to determine the expected number of Salmonella infections and illnesses resulting from a drinking water--wastewater cross-connection incident using data generated from a distribution system simulator study and compared our results to a reported cross-contamination event that occurred in Pineville, Louisiana in 2000. Probabilities of infection and illness were estimated for different exposure scenarios representing different Salmonella concentrations and the characteristic varied attack rates for waterborne Salmonella. Risks of Salmonella infection range from 10% after a 1 day exposure (assuming the lower bound Salmonella concentration) to a 1-log greater risk of infection for all other scenarios, with risks of infection approximately 99% for 30 and 90 day exposure durations.

Key words: cross-connection, Salmonella, quantitative microbial risk assessment.

Resume : L'evaluation quantitative du risque microbien est une maniere utile de predire l'incidence d'infections et de maladies au sein d'une communaute suivant l'exposition a des pathogenes. Nous avons utilise cette technique d'evaluation des risques afin de determiner le nombre prevu d'infections et de maladies a la Salmonella decoulant d'un incident de connexion croisee entre l'eau potable et les eaux usees, en utilisant les donnees generees a partir d'une etude de simulation de systeme de distribution; nous avons par la suite compare nos resultats a un evenement rapporte de contamination croisee qui est survenu a Pineville, en Louisiane, en 2000. Les probabilites d'infection et de maladies ont ete estimees pour differents scenarios d'exposition representant differentes concentrations de Salmonella et pour des taux d'attaque variables pour la Salmonella dans l'eau. Les risques d'infection a la Salmonella variaient de 10 % apres une exposition d'une journee (en assumant une concentration de Salmonella dans la limite inferieure) a un risque d'infection superieur de 1 log a tous les autres scenarios, avec des risques d'infection d'environ 99 % pour des durees d'exposition de 30 et de 90 jours.

Mots-cles : connexion croisee, Salmonella, evaluation quantitative du risque microbien.

[Traduit par la Redaction]

Introduction

Waterborne disease occurs in developed countries as well as in developing countries due to either suboptimal treatment of drinking water or problems within the drinking water distribution system. Disease outbreaks associated with distribution system issues may be due to a cross-connection where a potable water distribution system comes in contact with a nonpotable source. Under certain conditions, back flow may occur where a nonpotable (contaminated) source enters the potable distribution system thus creating the opportunity for disease-causing microorganisms (pathogens) to be present in water used by consumers for drinking, bathing, cooking, and other purposes. Backflow contamination due to cross-connections has been associated with a variety of sources including sewer lines, drain lines, untreated or reclaimed water sources, among others (Manual of Cross Connection Control 1993).

Despite significant advances in technology, microbial-related waterborne disease outbreaks continue to occur in the United States. The Centers for Disease Control and Prevention documented 57 waterborne disease outbreaks due to backflow contamination from 1981 to 1998 that led to 9734 illnesses (USEPA 2002). Twenty of these outbreaks and 65% of the reported illnesses were caused by pathogens, with the remaining outbreaks due to chemical contamination or unidentified causes. The United States Environmental Protection Agency's (USEPA) Health Effects Research Laboratory reports that from 1920 to 1980 cross-connections and backflow were the cause of 78% of waterborne outbreaks associated with distribution system problems in the United States, subsequently causing 95% of waterborne illness cases (AWWA 1990). …

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