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
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.

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

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 = 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…