| Abstract
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The FAST-ELISA and modified Ritchie concentration technique were used in a comparative study assessing incidence of Schistosoma mansoni infection among children from Halaba, Egypt (HE), Kaundama, Malawi (KM), and Mtayangoma, Malawi (MM). FAST-ELISA had a sensitivity ranging from 90% to 100%. At HE, KM, and MM, seroprevalence (59.8%, 82.7%, and 89.9%, respectively) was higher (p < 0.001) than parasitologic prevalence (22.7%, 28.6%, and 54.3%, respectively). FAST-ELISA was more sensitive in detecting new infections than stool exam; "crude" serologic incidence rates were 11.9%, 47.1%, and 38.9%, compared with coprologic incidence rates of 4.2%, 11.9%, and 20% at HE, KM, and MM, respectively. 97% of stool conversions occurred in children who were seropositive on first exam, suggesting many were already infected but stool-negative before the transmission season. Only 0.5% (HE), 4.5% (KM), and 3.7% (MM) of stool-negative children had more than 4 eggs/g after conversion. Children who seroconverted had pretransmission geometric mean antibody (GMA) levels similar to stool-positive children, but higher (p < 0.030) than stool-negative children. Coprologic and serologic conversion:reversion ratios agreed with other measures of transmission. GMA level provided an indirect measure of intensity of infection and indication of transmission level within and between communities. GMA increased with geometric mean egg count (GMEC) among infected children at HE (r = 0.2896, p < 0.01) and MM (r = 0.3197, p < 0.01), but not at KM. Comparisons of GMA level, with either GMEC or stool prevalence indicated a significant correlation between GMA and the other 2 more conventional indices of infection. Within 10 days of treatment, GMA increased over pretreatment level (p = 0.00005) but fell to pretreatment level four months later in children who were still stool-positive. Among treated children, stool-negative four months posttreatment, GMA was lower than pretreatment level (p = 0.0037). FAST-ELISA provides an objective measure of incidence and a more convenient, rapid, and sensitive epidemiologic tool than stool examination for assessing schistosomiasis transmission.
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