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 / 中国血吸虫病防治杂志

ABSTRACT

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.