TABLE 1.
Summary of samples used in the development and validation of the field coAg ELISAa
| Characteristic | Phase I: test development | Phase II: small-scale validation | Phase III: large-scale validation | Phase IV: colorimetric scale evaluation |
|---|---|---|---|---|
| Objective | Identify optimal conditions for modified field coAg ELISA | Compare field and standard coAg ELISA results on a small set of known samples | Compare field and standard coAg ELISA results on a large set of known samples | Compare field coAg ELISA results using a spectrophotometer to those using a colorimetric scale |
| Stool sample source | Archived samples that were previously typified | Archived samples that were previously typified | Samples that were typified during the Cysticercosis Elimination Evaluation (15) | Archived samples that were previously typified |
| Year | 2004 | 2004 | 2009 | 2012 |
| Sample selection process | Samples were selected to generate a positive pool (P1) and a negative pool (N) | Available samples that had sufficient volume (≥30 mL of supernatant) | Systematic sampling among available samples (n = 48,648) | Available samples that had sufficient volume (≥30 mL of supernatant) |
| Positive samples | Confirmed diagnosis by microscopy, PCR, and/or gravid proglottids | coAg ELISA (PP ≥ 7.5) | coAg ELISA (positive/suspect, PP ≥ 14; weakly suspect, PP 7.5–14) | coAg ELISA (PP ≥ 7.5) |
| Negative samples | coAg ELISA (PP < 7.5) | coAg ELISA (PP < 7.5) | coAg ELISA (PP < 7.5) | coAg ELISA (PP < 7.5) |
| Selected study samples | Positive, 69; negative, 46 | Positive, 80; negative, 80 | Positive/suspect, 357b; weakly suspect, 261; negative, 737b | Positive, 308; negative, 56; T. saginata, 78 |
| Total no. of study samples | 115 | 160 | 1,355 | 442 |
Abbreviations and definitions: coAg ELISA, coproantigen enzyme-linked immunosorbent assay. Optical density (OD) values were read using a spectrophotometer (Molecular Devices Vmax) at 650 nm. Strong positive pool (P1) is the mean OD from a group of positive samples selected from participants with confirmed Taenia solium diagnosis. P1 was compared to historical P1s to ensure equivalence over time. Negative pool (N) is a group of randomly selected negative samples from regions of endemicity and regions of nonendemicity. Percentage of positivity (PP) is calculated as the OD of the sample/(OD of P1) × 100.
PCR-restriction enzyme analysis (PCR) was used for species-specific diagnosis when proglottids, scolexes, or visible parasite material was present in the stool sample (n = 51). Among the positive/suspect samples, 33 were confirmed as T. solium. One sample in the weakly suspect and 17 in the negative category were T. saginata.