The Implemental Research On The Integrated Control Strategy Of Schistosomiasis With An Emphasis On Source Of Infection In Mountainous Areas Of Yunnan Province

The study sites were located in Eryuan County including four villages in two types of schistosomiasis endemic areas, namely dam area and mountain area. Xinlian Village in dam areas and Qieye Village in mountainous areas were selected as experimental group where integrated strategy with an emphasis on control of infection sources was implemented. Meanwhile, Yonglian Village in dam areas and Qiandian Village in mountainous areas were selected as control group where conventional control measures were undertaken. The control effect between the two groups from 2005 to 2007 was compared, and both cost-effectiveness and cost -benefit were analyzed along with the impact factors. Then the applicability and practicability in mountainous areas of the aforementioned integrated strategy were elucidated, in order to provide scientific basis to the establishment and adjustment of the strategy for schistosomiasis control.Based on the epidemic factors and characteristic of schistosomiasis transmission in mountainous areas of Yunnan province, the integrated control strategy with stressing on safe water supply and sanitation, fencing domestic animals, construction of methane-generating pits and prohibiting grazing in snail habitats was carried out in experimental groups. The conventional control measures, such as snail survey and elimination, human and domestic animal infection survey, and chemotherapy and health education given to villagers were performed in control group. Retrospective investigation and field survey were applied respectively to collect information on control measures and endemic status of schistosomiasis in the four villages mentioned above from 2005 to 2007. The unit cost and its composition of each measure in the two villages of experimental group in 2007 was obtained, while those in the 2005 and 2006 were calculated according to the corresponding rate of discounts. Then the unit cost was multiplied by workload to get the cost of each measure, and the sum of all measures was considered as the total cost of village in the year. After verifying the cost of 2007 according to the actual cost from the accounting statements in Eryuan County in the year, the error between the actual and calculated value was obtained. Then the error was used to correct the cost of each year. In addition, two rounds of Delphi method was developed in order to select the evaluation indices which were more suitable for mountainous areas. The evaluation indices for control effect assessment were picked out in the first round, and the weight coefficients for each index were determined in the second round. Then the formula for Schistosomiasis Control Effectiveness Index (SCEI) calculation was established by using the weight coefficients. On the foundation of the analysis and comparison of control effect between experimental and control groups, the factors which significantly influenced the control effect were selected after multiple regression analysis was performed. As the following, cost-effectivenesses and cost-benefits of both two groups were analyzed by calculation of cost-effectiveness ratio and benefit-cost ratio (BCR). Subsequently, the sensitive factors of the benefit were selected for both the integrated strategy and the conventional measures by net discounting value method in the sensitivity analysis. Finally, the combination approaches appropriate for the control of schistosomiasis in mountainous areas were put forward according to the results of study.Through studying on the average unit cost of schistosomiasis control measures in 2007, we could find that the unit cost in mountainous areas was higher than that in dam areas for all the measures. The salary and allowance of the staff accounted for about 45% of the unit cost, and as to the casual laborers, the proportion was about 15%. The error was 22.47% by comparing between the calculated cost of schistosomiasis control programme in both dam and mountainous areas of Eryuan County in 2007 and the accounting statement of Eryuan County in 2007, the former was about 20% higher than the latter.Results showed that infection of resident, domestic animal and snail with Schistosoma japonicum were selected as the primary indices for evaluation, and then-weight coefficients were 0.32, 0.36 and 0.32, respectively. Six indices including infection rates of resident, children younger than 14 years old, domestic animal and snail, the density of infected snail and living snail were determined as the secondary indices, and their weight coefficients were 0.55, 0.45, 1, 0.35, 0.35 and 0.30, respectively. The formula established to calculate SCEI based on the indices and their weight coefficients was as follows:SCEI=(decreased percentage of resident×0.55+ decreased percentage of children younger than 14 years old×0.45)×0.32 + decreased percentage of the infection rate of bovine×0.36+( decreased percentage of the density of living snail×0.3+ decreased percentage of the density of infected snail×0.35+decreased percentage of the infection rate of snail×0.35)×0.32The infection rates of resident, children younger than 14 years old, bovine and snail and the density of infected snail in both experimental group and control group were decreased by different degree in 2007 comparing with those in 2005. The infection rates of Xinlian and Qieye Village in experimental group were decreased by 93.36% and 96.44%, respectively, and the decreased percentages of Yonglian and Qiandian Village in control group were 83.24% and 84.38%, respectively. The extent of decrease in experimental group was significantly higher than that of control group with a P value below 0.001. The SCEI of Xinlian and Qieye Village in experimental group were 82.52 and 83.44, respectively; and that of Yonglian and Qiandian Village in control group were 61.67 and 70.46, respectively. The experimental group had a higher SCEI compared to the control group.The infection rate of bovine and the coverage rate of methane-generating pit were two main factors affecting the infection rate of resident. When Y was the infection rate of resident, X₁ was the infection of bovine and X₂ was the coverage rate of methane-generating pit, then the regression equation namely(?) = 7.113 + 0.523X₁ -0.166X₂ could be established. Meanwhile if (?) was the infectionrate of children younger than 14 years old, X₁ was the infection rate of bovine and X₂ was the coverage rate of sanitary latrine, thus another regression equation namely(?) = 4.945 + 0.502X₁ - 0.153X₂ could be established. It suggested that the schistosomiasiscontrol in mountainous areas should put emphasis on the domestic animal schistosomiasis control and the enlargement of the coverage of methane-generating pit and sanitary latrine.The result of cost-effectiveness analysis showed that if the infection rate of every 100 people decreased by 1%, the cost of experimental and control group in dam areas would be 173.43 Yuan and 161.91 Yuan, respectively, the difference between the two groups was not significant. While in mountainous areas, the cost of the two groups would be 265.55 and 405.11 Yuan, respectively, the cost in experimental group was significantly lower than that in the other group. In dam areas, the cost for SCEI to increase by every one Unit of experimental and control group were 6614.32 Yuan and 6433.71 Yuan, respectively, the former was slightly higher than the latter. While in mountainous areas, the cost of the two groups were 4696.00 Yuan and 6976.31 Yuan, respectively; the former was better than the latter.The result from cost-effectiveness analysis showed that BCR in dam areas in the experimental and control group were 11.82 and 13.10, respectively; while in mountainous areas the BCR of the two groups were 4.52 and 4.07, respectively. The result from the sensitivity analysis revealed that BCR of both experimental group and control group were above 1 when the infection rate of resident was higher than 5%; when the infection rate decreased to 3%, BCR of the two villages in control group came to below 1(0.42 and 0.45, respectively); furthermore, if the rate dropped to 1%, the BCR of both the two groups would fall to below 1, so to implement this strategy was not worthwhile economically.In conclusion, the integrated control strategy focusing on infectious sources control has better control effects and benefits comparing to the conventional control strategy. The main factors affecting the control effects include the infection rate of bovine and the coverage rate of both methane-generating pit and sanitary latrine. The factor to which the control benefits are most sensitive is the infection rate of resident. When the rate is not below 3%, the integrated control strategy is feasible on economic point and is fit to apply in endemic regions of mountainous areas.