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Quantitative microbial risk assessment of drinking water in San Cristóbal de Las Casas, Chiapas, Mexico.

Abstract:

The city of San Cristobal de Las Casas, Chiapas, Mexico lacks information on the microbiological quality of the municipal drinking water distribution system. Therefore, the risks associated with its intake and the impact it has on public health is unknown. This study assessed the risk of microbial contamination from the Potable Water and Sewerage Municipal (SAPAM) water sources, by conducting a Quantitative Microbiological Risk Assessment (QMRA). Samples from each source were analyzed for Escherichia coli. The QMRA and disease burden were calculated using estimates of the concentrations of four reference pathogens (E. coli O157:H7, Campylobacter, rotavirus and Cryptosporidium) based on published ratios between E. coli and the indicated pathogens. All sources showed fecal contamination. The annual probability of infection was higher than the safety threshold set by the EPA on all previously indicated pathogens. The sum of the disease burden was 2.40 × 10-3 DALYs per person per year, much higher than WHO reference level. The risk was not uniform for the entire population, inequalities in the exposure and the risk were found according to the source of supply. This study demonstrates the need to implement improvements in drinking water distribution system to reduce the public heath risk.