[Risk Assessment of Schistosomiasis Transmission by Catalytic Models Based on Antibody Positive Rates].

Abstract

Objective: To evaluate the transmission risk and features of schistosomiasis by analyzing the data concerning positive rates of anti-schistosome antibody using catalytic models.

Methods: Cross-sectional survey was conducted in seven villages with different endemicity of schistosomiasis in Jiangxi (Caohui, Xinhua, Jingtou villages), Anhui (Yuye, Tieguai, Longshang villages) and Hubei (Hebei village) Provinces in 2008. Serum samples were collected and indirect hemagglutination assay was performed to detect anti-schistosome antibodies in serum. Antibody positive rate was calculated and differences among villages and age groups as well as between genders were analyzed. Data of antibody positive rate based on age strata for each village were analyzed by two-stage catalytic model and reversible and two-stage compound catalytic model. Parameters of each model were estimated through the maximum likelihood method. Seroconversion rate and sero-negative conversion rate were estimated in the two-stage catalytic model. Seroconversion rate, seroreversion rate and sero-negative conversion rate were estimated in reversible and two-stage compound catalytic model. The fitting effect was evaluated through correlation analysis and chi-square tests. The best fitted models and parameters were used to analyze the transmission risk and characteristics of schistosomiasis.

Results: A total of 6 428 individuals were examined with an average schistosomiasis antibody positive rate of 39.80%（2 485/6 428）. In terms of age, the peak of antibody positive rate in Caohui, Xinhua, Jingtou, Yuye, Tieguai, Longshang, and Hebei villages occurred in the age group of 46-50 （82.86%, 58/70）, 31-35 （60.78%, 31/51）, 31-35 （68.42%, 26/38）, 41-45（55.04%, 71/129）, 51-55 （62.38%, 63/101）, 56-60 （31.43%, 33/105）, and 16-20 （21.88%, 7/32） years old, respectively. In general, the antibody positive rate showed a trend of increase followed by a decrease with increasing age in each village. The best model for the data of Caohui, Xinhua and Jingtou and Yuye village was the two-stage catalytic model. The estimated seroconversion rate in these villages was 0.049 5, 0.044 0, 0.055 7, and 0.034 4 respectively, all higher than the corresponding sero-negative conversion rate of 0.005 9, 0.019 6, 0.015 5, and 0.017 8. The best model for the data of Longshang, Tieguai and Hebei villages was the reversible and two-stage compound model. The seroconversion rate in these villages was 0.062 9, 0.168 1, and 0.039 4 respectively, the seroreversion rate was 0.168 8, 0.121 1, and 0.152 2, and the sero-negative conversion rate was 0.001 7, 0.000 2, and 0.090 9.

Conclusions: The catalytic model based on antibody positive rate by age strata could reflect the transmission rate and risk quantitatively and may provide guidance for making control strategies.