QUANTITATIVE RISK ASSESSMENT OF SALMONELLA SPP. IN SURFACE WATER OF THE RIVER, CENTRAL PART THAILAND.

Abstract

Salmonella spp. is transmitted via fecal oral route and readily spread into the environment. The information regarding risk of utilizing the surface water in the Central and West Thailand as a source of tap water associated with either feces or manure was limited. Quantitative microbial risk assessment has been used to estimate the risk of waterborne salmonellosis. For hazard characterization, the beta Poisson model was employed to describe the causal relationship between dose of Salmonella from water exposure and its effect as salmonellosis. Prevalence and concentration of Salmonella in the surface water including water exposure were used to model the probability of exposure. The risk characterization was the integration of both hazard characterization and exposure assessment. The probabilistic prevalence was described by beta distribution. The surface water as a resource of MWA tap water were collected 1000 ml and then detected Salmonella spp. by ISO 6579. The range of mean Salmonella prevalence of the surface water along rivers was between 8.33% and 33.33%. Whereas the mean concentrations of Salmonella in the surface water were between -4.03 and -3.45 log MPN/ml. The water exposure of population by the river bank was about 0.91 liter/year. The risk estimates from all sampling locations along rivers fell into 4 risk levels where the mean of salmonellosis of risk levels 1, 2, 3 and 4 was 399, 526, 1,337 and 2,619 cases/year, respectively. The risks of salmonellosis in the surface waters from upstream were less fluctuating than those in the surface water from the downstream of rivers of Central and West Thailand. The majority of serovar was non-Typhiodal Salmonella. Although the same Salmonella serovar was identified from upstream to downstream of the same river yet across sampling rounds. This study provided essential and background health risk levels from surface water exposure and were crucial for the national or local authorities to prepare risk mitigation measures for a long term risk management plan or emergency plan in case of waterborne disease outbreaks.