Chagas' disease: an algorithm for donor screening and positive donor counseling

Abstract

Classical serological screening assays for Chagas' disease are time consuming and subjective. The objective of the present work is to evaluate the enzyme immuno-assay (ELISA) methodology and to propose an algorithm for blood banks to be applied to Chagas' disease. Seven thousand, nine hundred and ninety nine blood donor samples were screened by both reverse passive hemagglutination (RPHA) and indirect immunofluorescence assay (IFA). Samples reactive on RPHA and/or IFA were submitted to supplementary RPHA, IFA and complement fixation (CFA) tests. This strategy allowed us to create a panel of 60 samples to evaluate the ELISA methodology from 3 different manufacturers. The sensitivity of the screening by IFA and the 3 different ELISA's was 100%. The specificity was better on ELISA methodology. For Chagas disease, ELISA seems to be the best test for blood donor screening, because it showed high sensitivity and specificity, it is not subjective and can be automated. Therefore, it was possible to propose an algorithm to screen samples and confirm donor results at the blood bank.<br>Os testes sorológicos clássicos utilizados na triagem de doadores de sangue são trabalhosos e subjetivos. O objetivo do presente trabalho é o de avaliar a metodologia imuno-enzimática (ELISA) e propor um algorítmo para doença de Chagas em bancos de sangue. Foram estudados 7999 doadores de sangue e/ou componentes cujas amostras foram testadas com o objetivo de tria-las sorologicamente para doença de Chagas utilizando hemaglutinação passiva reversa (RPHA) e imunofluorescência indireta (IFA). As amostras reativas em pelo menos uma destas metodologias, foram retestadas com reativos diferentes por RPHA, IFA e fixação de complemento (CFA). Esta estratégia nos permitiu criar um painel de 60 amostras com as quais tornou-se possível a avaliação do método imunoenzimático (ELISA). A sensibilidade da triagem dos doadores pelos métodos ELISA e IFA foi de 100%. A especificidade foi melhor para a metodologia imunoenzimática. O teste ELISA parece ser o ideal para triagem em bancos de sangue pois é altamente sensível, específico, não é subjetivo e pode ser automatizado. Desta forma, torna-se possível a formulação de um algorítimo a ser utilizado na triagem sorológica e confirmação de resultados em doadores de bancos de sangue

Safety of the Blood Supply in Latin America

“…The reported confirmation rates for HBV in developed countries are 34% (92) and 38.8% (49); the latter rate was selected for use here. The confirmation rate selected for HCV was 50%, consistent with the median of what has been previously reported (49,92,94,106), and the confirmation rate selected for T. cruzi was 25% (31). Calculations for HIV were also adjusted on the basis of a report from Southern Brazil, with case confirmation similar to that mentioned above, indicating an estimated residual risk of 1 in 50,000 because of the window period (36).…”

“…With T. cruzi, since there is no single test that can be used as a confirmatory test, it is assumed that a true-positive unit is one that is positive by more than one test (69,83). Following these criteria, the rates of true positives for T. cruzi among blood donors may vary from 25% to more than 90% (31,81,83).…”

Chagas' heart disease

“…These are figures that thoroughly substantiate the concept that elimination of Chagas' disease vectorial (by improving the quality of housing and use of residual insecticides) and of transfusional transmission in both endemic and nonendemic areas [11][12][13] , is a highly cost-effective public health policy 7,10 . Despite being hindered by financial limitations, these goals have been attained in scattered regions [14][15][16] .…”

Control de la infección por Trypanosoma cruzi en donantes de sangre de Colombia, 2003.

“…Es importante destacar que sólo tenemos una visión parcial de lo que ocurre con respecto a la vigilancia realizada por los LSP, dado que no se realiza confirmación a todas las unidades reactivas y la información no es enviada a tiempo, lo que resulta en menos oportunidad o pérdida para el diagnóstico, asesoria y tratamiento de estas personas, y facilita la difusión de esta infección a la población general en caso de tratarse de donantes verdaderamente infectados, dificultando así el control epidemiológico de la enfermedad (18,(22)(23)(24) Casanare y Arauca tamizaron todas sus unidades de sangre, pero presentaron reactividad elevada a T. cruzi (7,2% y 2,7%, respectivamente). Sólo Casanare realizó confirmación de donantes reactivos mientras que Arauca no confirmó ninguno de sus 40 casos; además, sólo uno de los tres bancos de estos departamentos evaluó su desempeño a través del PEED; estos hallazgos permiten deducir que el mayor riesgo de adquirir una infección por Chagas transmitida por transfusión (ITT) y de difundirla en la comunidad se presenta en estos departamentos (4,9,18-19).…”