Quantitative microbial risk assessment of water consumption in flood-prone communities, Nakhon Si Thammarat province, Thailand

Abstract

A cross-sectional study was performed for household survey using a questionnaire with a face-to-face interview to determine the general characteristics and water consumptions during flooding events in flood-prone communities, Pak Phanang and Chian Yai district, Nakhon Si Thammarat province, Thailand between February-July 2020. From a 425 household survey, 69.5% were female, two-thirds of the participants aged 46 years old and above, and had the average monthly household income at 7305.13 ± 7016.56 Baht. Free bottled water and stored water in their own houses were the two main sources of drinking water during floods. ​From the survey, stored rainwater typically collecting via roof tiles or pipes were used for drinking and cooking during floods in the study community. 28 stored water samples were collected to determine the water quality through turbidity and microbial indicator and to estimate the health risk from consumption of stored water using QMRA. E. coli, a fecal indicator, was used to estimate the presence of Cryptosporidium oocysts in the water samples. The results show that 27 out of 28 water samples passed the turbidity standard from WHO for drinking water (≤ 5NTU). Whereas, the total coliform bacteria found from 12 samples ranging from 5 CFU/mL to 235 CFU/mL. Only two samples had E.coli contamination at 1 and 2 CFU/mL. In this study, the QMRA was conducted to examine the probability of disease pppy of Cryptosporidium infection. A ratio of E. coli: Cryptosporidium was applied to estimate the contamination of Cryptosporidium oocysts from the samples. The exponential model was used for dose-response relations of Cryptosporidium infection. The route of exposure was the ingestion of drinking water, which assumed to be 2L/person/day in adults. It was estimated to have 0.02 oocyst /1L of stored water. The probability of infection with Cryptosporidium oocysts in a single exposure for adults was 0.000168. After performing risk characterization, the study found that the probability of disease per person per year was 7.858 x 10-3. From the results, a disease risk of 10-3 per person per year indicated that 0.1% of the people in the study area would get infected with the disease annually from drinking the stored water.