[Study on cut-off value of IHA method for schistosomiasis diagnosis in different endemic areas]

To explore the cut-off value of the indirect haemagglutination test (IHA) method for schistosomiasis japonica diagnosis in different endemic areas.

Totally 55 nature villages of the lake-type endemic counties, Yugan and Xinzi, in Poyang Lake Region of Jiangxi Province were chosen as the study fields, and all the villagers over 5 years old were parallelly examined by Kato-Katz method + miracidial hatching test and IHA method. The detection data were analyzed by the correlation analysis, and the threshold values of the IHA method in different endemic areas were decided by the receiver operating characteristic (ROC) curve.

The positive rate of stool examinations of the villagers was correlated with the distribution trend of the antibody level of whole population (r = 0.588, P ＜ 0.05), but no correlation with the antibody level of the positive population (r = 0.221, P ＞ 0.05). The antibody level of stool-negative population during the period of 2008 to 2011 detected by IHA method dropped year by year, and the annual difference was statistically significant (F = 3.650, P ＜ 0.05). While the antibody level of stool-positive population found during the period of 2008 to 2011 maintained a certain high level in the 4 years, and there was no statistically significant difference among them (F = 2.461, P ＞ 0.05). When the positive rates were <1%, 1%-5% or >5%, the specificity of diagnosis could be improved when 1∶80, 1∶20 and 1∶10 were used as the cut-off values of IHA correspondingly.

The different threshold values for diagnosis of schistosomiasis japonica should be considered while using IHA method to screen out patients in different endemic areas.