Quantitative microbial risk assessment of Salmonella in surface water as a source of tap water

Abstract

Salmonella spp. is fecal-orally transmitted and readily spread into the environment. Little is known about risk of utilizing surface water in Thailand. Quantitative microbial risk assessment has been used to estimate the risk of waterborne salmonellosis. For hazard characterization, beta-Poisson model was employed to describe the relationship between dose of Salmonella from water exposure and salmonellosis. Prevalence and concentration of Salmonella in the surface water including water exposure were used to model probability of exposure. The probabilistic prevalence was described by beta distribution and the range of mean Salmonella prevalences of the surface water along rivers were between 8.33% and 33.33%. The mean concentrations of Salmonella in the surface water were between -4.03 and -3.45 log MPN/ml. The risk estimates from all sampling locations along rivers fell into 4 risk levels 1, 2, 3 and 4 of which the means of salmonellosis were 399, 526, 1,337 and 2,619cases/year, respectively. The risks of salmonellosis in the surface water upstream less fluctuated less than that downstream in Central Thailand. The risks of salmonellosis in the surface water samples nearby livestock farm areas were not clearly related to animal production.