The epidemiology of enteric infections in agricultural communities exposed to wastewater irrigation: Perspectives for risk control

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Abstract
A cross-sectional survey was carried out in the irrigation districts of central Mexico, in which 9435 individuals participated. The health outcomes included diarrhoeal diseases and Ascaris lumbricoides infection. Water quality was assessed using faecal coliforms (FC) and nematode eggs as indicators of faecal pollution. Exposure groups were: 848 households irrigating with untreated wastewater; 544 households irrigating with the effluent from a series of interconnected reservoirs; and 928 households farming with natural rainfall. Children from households irrigating with untreated wastewater (108 FC/100 mL and 125 nematode eggs/L) had a 33% higher risk of diarrhoeal diseases than children from rainfall villages (OR = 1.33), whereas children from households exposed to the reservoirs effluent were not different from those in the rainfall group (OR = 1.17). No excess risk was found in older individuals from different exposure groups, but males had a 50% higher risk of disease than females (OR = 1.50). In the final analysis, drinking unboiled water and cultivating vegetables crops were associated with a higher risk of disease, both in children and older individuals, (OR = 1.45 and 2.00, respectively). Children from households exposed to untreated wastewater showed a fivefold increase in risk of A. lumbricoides infection (OR = 5.71), when compared to children from rain-farming villages. The observed difference in older individuals was even higher (OR = 13.18). Such risk, however, was substantially reduced in individuals exposed to the reservoirs effluent (OR = 1.29 and 1.94) with no detectable ova. The final analysis showed that most infected individuals came from landless households, poorer dwellings and low standards of sanitation, often purchasing vegetables in local shops (OR = 2.20, 2.23, 1.72 and 1.43, respectively). These results are discussed in the context of health protection measures and policy recommendations.