Contribution of Wastewater Irrigation to Soil Transmitted Helminths Infection among Vegetable Farmers in Kumasi, Ghana

Wastewater irrigation is associated with several benefits but can also lead to significant health risks. The health risk for contracting infections from Soil Transmitted Helminths (STHs) among farmers has mainly been assessed indirectly through measured quantities in the wastewater or on the crops alone and only on a limited scale through epidemiological assessments. In this study we broadened the concept of infection risks in the exposure assessments by measurements of the concentration of STHs both in wastewater used for irrigation and the soil, as well as the actual load of STHs ova in the stool of farmers and their family members (165 and 127 in the wet and dry seasons respectively) and a control group of non-farmers (100 and 52 in the wet and dry seasons, respectively). Odds ratios were calculated for exposure and non-exposure to wastewater irrigation. The results obtained indicate positive correlation between STH concentrations in irrigation water/soil and STHs ova as measured in the stool of the exposed farmer population. The correlations are based on reinfection during a 3 months period after prior confirmed deworming. Farmers and family members exposed to irrigation water were three times more likely as compared to the control group of non-farmers to be infected with Ascaris (OR = 3.9, 95% CI, 1.15–13.86) and hookworm (OR = 3.07, 95% CI, 0.87–10.82). This study therefore contributes to the evidence-based conclusion that wastewater irrigation contributes to a higher incidence of STHs infection for farmers exposed annually, with higher odds of infection in the wet season.污水灌溉兼具多重应用益处，但同时也可能引发严重的健康风险。此前针对农民群体因土源性蠕虫（Soil Transmitted Helminths, STHs）感染所面临的健康风险评估，多通过单独检测污水或作物中的污染物含量进行间接推断，仅极少数研究借助流行病学手段开展过有限规模的正式评估。本研究拓宽了暴露风险评估中感染风险的考量范畴：不仅检测了灌溉用水及耕层土壤中的土源性蠕虫浓度，还对农民及其家庭成员（湿季样本量165、干季127）与非农民对照组（湿季样本量100、干季52）粪便中的土源性蠕虫卵实际载荷量进行了定量测定。本研究针对接触污水灌溉与未接触该灌溉方式的两组人群，分别计算了比值比（Odds Ratio, OR）。研究结果显示，灌溉用水与土壤中的土源性蠕虫浓度，与暴露群体粪便中检测到的土源性蠕虫卵含量呈显著正相关，该相关性基于研究对象在既往经确认完成驱虫治疗后3个月内发生的再次感染情况得出。与非农民对照组相比，接触灌溉污水的农民及其家庭成员感染蛔虫（OR=3.9，95%置信区间CI：1.15–13.86）与钩虫（OR=3.07，95%CI：0.87–10.82）的风险分别为对照组的3.9倍与3.07倍。因此，本研究为以下循证结论提供了实证支撑：每年长期接触污水灌溉的农民，其土源性蠕虫感染发生率更高，且湿季的感染风险比值比进一步升高。