Quantitative Microbial Risk Assessment of Campylobacter for roof-harvested rainwater domestic use

Roof harvested rainwater (RHRW) use has become a very widespread technique in Brazilian rural communities, especially in regions with low water security. Since 2003, more than 500,000 cisterns were built in order to provide access to fresh water for communities in the Northeast region alone. Seeking to address the health concerns that may arise from this practice, the present study evaluated the microbiological risk for roof-harvested rainwater (RHRW) domestic use, with Campylobacter as the pathogenic microorganism of reference, through a Quantitative Microbial Risk Assessment (QMRA). QMRA has been widely used as an alternative method for epidemiological assessment of human exposure to microorganisms that can cause diseases, through a four-step process: (i) hazard identification, (ii) exposure assessment, (iii) dose-response assessment, and (iv) risk characterization. The results presented drinking as the water use with the highest risk, with 3.4 x 10^-04 DALY per person per year, and, in decreasing order: bathing, food washing, hose irrigation and toilet flushing, with values for median risk of 6.5 x 10^-07, 4.0 x 10^-07, 2.1 x 10^-07 and 1.4 x 10^-07 DALY, respectively. Therefore, drinking would be the only water use that would require preliminary treatment for its safe use, considering the acceptable risk standards set by the World Health Organization. When associated with the use of simple protection barriers, such as clay filters and first flush devices, it was observed that would be possible to achieve even safer values, reaching 2 x 10^-06 for intentional rainwater intake, which would already be close to the limit imposed as safe, confirming the efficiency of these measures.