Presentation on theme: "Field evaluation of a rapid immunochromatographic assay for detection of Trypanosoma cruzi infection by use of whole blood 1. Médecins Sans Frontières."— Presentation transcript:
Field evaluation of a rapid immunochromatographic assay for detection of Trypanosoma cruzi infection by use of whole blood 1. Médecins Sans Frontières – Spain 2. Universitario de Medicina Tropical - Universidad Mayor de San Simon, Bolivia 3. Instituto Oswaldo Cruz - Fiocruz, Rio de Janeiro, Brazil Paul Roddy June 2008
Study Rationale Sensitivity and specificity when using whole blood was unknown. Circumvent constraints associated with conventional serological assays and bolster Chagas disease control efforts.
Objectives Evaluate Measure Compare
Methods (1/4) - study location and participants April – June 2007 Valle Hermoso district - Sucre municipality (pop. = 46,000) 9-months to 17.9 years (pop. = 19,000)
Methods (2/4) – diagnostic test procedures 3.5 millilitres (mL) of whole blood. 2 out of the 3 conventional assays are positive. Benznidazole treatment offered. 10 microliters (µL) of whole blood. Independently interpreted at 15 minutes.
Methods (3/4) – laboratory quality control Quality control applied at health clinic and laboratory levels. – –Calibrations – –Positive and negative serum controls – –Good practices check list – –Internal and external quality control
Methods (4/4) – measurements of diagnostic test performance Sensitivity and specificity calculated. The inter-observer reliability measured = kappa statistic. The ease of use criterion were quantified and compared.
Results – demographics 1,913 study participants M:F ratio = 0.95 Mean age = 9.3 years (SD= 4.4) Median age = 9.0 years (interquartile range = 6-13)
Results – sensitivity & specificity Stat- Pak Conventional Serology Positive Negative Total Positive Negativ e Total % sensitivity (95% CI: 87.4% %) 99.0% specificity (95% CI: 98.4% %)
Results – inter-observer reliability Trained, non-laboratory health workers concurred on 1,911 of 1,913 test results yielding: 99.9% overall agreement kappa =.999 (p<.0001)
Results – ease of use criterion Questionnaire items scored according to a scheme outlined in the Methods section of the article. Total of 51 possible points: Chagas Stat-Pak = points (77%) IHA assay = 34 points (67%) ELISA conventional = 30 points (59%) ELISA recombinant = 30 points (59%)
Possible limitation Cross-reactivity may occur between sera of patients infected with T. cruzi and sera of patients infected with Leishmania spp. when using conventional assays for the diagnosis of Chagasic infections. 8 / 121 = 6.6%
Conclusion and Recommendations (1/2) 1. 1.Effective laboratory-based solutions not widely available or likely to be anytime in the near future RDT cost remains out of reach for many impoverished people affected by the disease Compares less favorably with whole-blood RDT diagnosis of other parasitological vector-borne diseases.
Conclusion and Recommendations (2/2) 4. 4.Missed treatment opportunities and increased likelihood of chronic-stage disease sequela Not an ideal screening or diagnostic test for the population investigated in this study Hindered ability of the test to give dependable results under the conditions outlined in the study MSF continues to use whole blood with the Chagas Stat-Pak TM RDT…