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1. Médecins Sans Frontières – Spain

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  1. 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

  2. ELISA Conventional • IHA • ELISA Recombinant

  3. Study Rationale • Sensitivity and specificity when using whole blood was unknown. • Circumvent constraints associated with conventional serological assays and bolster Chagas disease control efforts.

  4. Objectives • Evaluate • Measure • Compare

  5. 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)

  6. 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.

  7. 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

  8. 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.

  9. 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)

  10. Stat-Pak Conventional Serology Positive Negative Total Positive 113 18 131 Negative 8 1774 1782 Total 121 1792 1913 Results – sensitivity & specificity 93.4% sensitivity (95% CI: 87.4% - 97.1%) 99.0% specificity (95% CI: 98.4% - 99.4%)

  11. 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)

  12. 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 = 39.25 points (77%) IHA assay = 34 points (67%) ELISA conventional = 30 points (59%) ELISA recombinant = 30 points (59%)

  13. 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%

  14. Conclusion and Recommendations (1/2) • 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.

  15. Conclusion and Recommendations (2/2) • 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-PakTM RDT…