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

ELISA Conventional IHA ELISA Recombinant

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 10 microliters (µL) of whole blood. Independently interpreted at 15 minutes. 3.5 millilitres (mL) of whole blood. 2 out of the 3 conventional assays are positive.   Benznidazole treatment offered.

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

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 = 39.25 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) 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) 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…