Circulating anodic antigen for detection of Schistosoma mansoni infection in Egyptian patients

We evaluated the ability of circulating anodic antigen (CAA) to identify infection with Schistosoma mansoni in a prospective cohort study of 257 Egyptian men, 147 with infection diagnosed by repeated Kato thick smears, and 110 without detectable infection. The CAA levels were obtained and the stool examinations were performed two weeks and one, two, four, and six months after praziquantel therapy for infected men. A CAA enzyme-linked immunosorbent assay was repeated twice on subjects who were otherwise negative for schistosomiasis. Circulating anodic antigen was detected in 117 cases, with an overall test sensitivity before treatment of 0.8. Sensitivity was related to the intensity of infection, ranging from 1.00 with > 400 eggs per gram (epg) of feces to 0.60 for those with < 100 epg. After praziquantel therapy, the level of the antigen was significantly reduced. Specificity was excellent before treatment (1.00, 95% confidence interval = 0.97-1.0), but it decreased to 0.98 four months after treatment. Likelihood ratios were significant for all titers > or = 4. We conclude that CAA has moderate sensitivity and excellent specificity when used to identify infection with schistosomiasis, as well as to monitor the results of therapy after at least one month after treatment.