日本血吸虫病常用诊断方法应用价值的评估Ⅱ IHA与Kato-Katz法结果的定量关系

目的分析IHA检测结果的群体特征与疫区疫情、传播状态或人群感染趋势的关系。方法采用Kato-Katz法（2粪6检）和IHA（定量检测）方法连续2年同时对1个血吸虫病疫区村常住居民进行调查,分析IHA的诊断效率、IHA阳性率和抗体水平变化与感染状态变化关系及血吸虫感染＂真阳性者＂和＂真阴性者＂的IHA抗体水平分布。结果以Kato-Katz法为金标准,IHA在疫区现场实际应用时,其敏感度较高,为77.27%～85.48%,阴性预测值〉94%;但特异度〈60%,且特异度随着年龄的增加而降低,在低年龄组人群（〈15岁人群）的特异度最高。IHA的人群抗体阳性率远高于粪检阳性率,但其年龄分布趋势与Kato-Katz法粪检阳性率的年龄分布一致。IHA的假阳性率为41.90%～44.56%,假阴性率为14.52%～22.73%。感染者（粪检阳性）治疗后,IHA的抗体阳性率下降缓慢,而且＂真阴性者＂和＂真阳性者＂的抗体水平分布有相当大的重叠。结论在我国目前疫情状态下,IHA在群体水平上更具应用价值,采用IHA对疫区人群查病宜注意同时存在＂扩大化疗对象＂和＂漏检传染源＂的问题,在目前血防＂达标＂进程中,现场应用免疫诊断方法时更应谨防其＂假阴性＂的出现。

Evaluation on application of common diagnosis methods for schistosomiasis japonica in endemic areas of China II Quantitive analysis of detection results for S. japonicum infection by IHA screening method and Kato-Katz technique

Objectives To explore the correlation between the population characteristics of sero-reactivity with quantitative antibody based-IHA and the transmission parameters,such as epidemic situation,transmission status or infection trend in population.Methods The residents in one endemic administrative village were simultaneously examined by Kato-Katz technique for parasitological stool examination,as well as by immuno-diagnostic technique IHA for detection of IgG antibody against soluble egg antigen for two consecutive years.The results of examination were analyzed and compared on the diagnostic parameters of IHA,the correlation of the changes of positive rates and antibody levels of IHA with the changes of infection trend in population and the distribution of antibody levels between 'the true negative' and 'the true positive'.Results When Kato-Katz technique based on 2 stool samples,each read in 3 thick smears,was used as the reference,the overall sensitivity of IHA was high (from 77.27% to 85.48%) with a relatively poor specificity of lower than 60%,the negative predict value (NPV) was excellent of higher than 94%.The specificity of IHA decreased with the increase of the age in different age-groups of population,showing the highest among the younger less than 15 years old.The distribution trends of positive rates of antibody in different age groups by IHA showed similar to that of egg positive rate detected by Kato-Katz although the positive rates of IHA were higher than these by Kato-Katz,which showed that a higher false positive (from 41.90% to 44.56%) and a certain false negative (from 14.52% to 22.73%)existed in IHA.The positive rate of antibody decreased slowly among the individuals with S.japonicum infection,who received treatment.There was an overlap in the distribution of antibody levels between ' the true negative' and ' the true positive'.Conclusions Under the current schistosomiasis epidemic situation in China,IHA is valuable in the epidemiologic surveys.It should be of further deliberation applying IHA as the screening approaches for identification of target individuals for treatment or determination of the infection rate in community and IHA needs to be combined with the parasitological examination.