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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

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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

slide2

ELISA Conventional

  • IHA
  • ELISA Recombinant
study rationale
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
Objectives
  • Evaluate
  • Measure
  • Compare
methods 1 4 study location and participants
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
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
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
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
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

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%)

results inter observer reliability
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
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
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
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
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…
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