Table 1.
Summary of assay validation data for the Salmonella Typhi Vi enzyme‐linked immunosorbent assay (ELISA)
| Analysis | Values |
|---|---|
| Intra‐assay imprecision (concentration) | % CV at different Typhi Vi concentrations |
| 12 U/ml | 6·3% |
| 34 U/ml | 4·1% |
| 38 U/ml | 4·3% |
| 59 U/ml | 6·5% |
| 90 U/ml | 4·6% |
| 128 U/ml | 3·7% |
| 197 U/ml | 3·2% |
| 343 U/ml | 3·9% |
| Interassay imprecision (concentration) | % CV at different Typhi Vi concentrations |
| 13 U/ml | 12·6% |
| 40 U/ml | 7·0% |
| 42 U/ml | 9·5% |
| 58 U/ml | 7·3% |
| 77 U/ml | 8·9% |
| 131 U/ml | 8·0% |
| 201 U/ml | 9·6% |
| 302 U/ml | 6·1% |
| Linearity | R 2, equation of best fit line |
| Sample 1 | R 2=0·99, y = 0·998 ± 0·013 U/ml |
| Sample 2 | R 2=0·99, y = 0·988 ± 0·015 U/m |
| Sample 3 | R 2=0·99, y = 1·00 ± 0·008 U/m |
| Sensitivity | Typhi Vi concentration (%CV)* |
| Sample 1 | 9 U/ml (range 8–10 U/ml), CV 5·9% |
| Sample 2 | 14 U/ml (range 13–15 U/ml), CV 3·4% |
| Interfering agent | Range of % interference |
| Chyle | −8·5 to 1·1% |
| Haemoglobin | −9·2 to 11·4% |
| Bilirubin C | −2·3 to 10·2% |
| Bilirubin F | −10·5 to 7·7% |
The % coefficient of variation (CV) for intra‐assay imprecision was calculated by running eight different concentrations of Typhi Vi immunoglobulin (Ig)G over 20 analyses in a single assay. The %CV for interassay imprecision was calculated by duplicate samples of eight different concentrations of Typhi Vi in six independent assays. Assay linearity (R 2, equation of best fit line), sensitivity (concentration, %CV) and interference analysis (% difference with addition of interfering substance) were performed as described in the Materials and methods.