TABLE 4.
Bayesian estimates of diagnostic sensitivity and specificity of the IFA in comparison to the ELISA (IDEXX) in detection of IgG and IgM antibodies to C. burnetii at a 1:160 dilution of goat seruma
| Antibody type(s) | Test | % sensitivity (95% PI) | % specificity (95% PI) | % prevalence 1 (95% PI) | % prevalence 2 (95% PI) | % agreementb (95% PI) | Kb (95% PI) | PABAKb (95% PI) |
|---|---|---|---|---|---|---|---|---|
| IgG phases 1 + 2 | IFA | 94.8 (80.3, 99.6) | 92.5 (77.1, 99.3) | 40.4 (26.0, 53.6) | 0.00 (0.00, 1.20) | 81.1 (72.7, 88.0) | 0.60 (0.43, 0.74) | 0.62 (0.45, 0.76) |
| ELISA | 70.1 (52.7, 91.0) | 96.2 (88.9, 99.2) | ||||||
| IgM phases 1 + 2 | IFA | 88.8 (58.2, 99.5) | 92.4 (83.0, 99.2) | 16.0 (8.6, 25.4) | 0.00 (0.00, 1.20) | 73.5 (64.5, 81.1) | 0.27 (0.09, 0.45) | 0.47 (0.29, 0.62) |
| modELISA | 71.7 (46.3, 92.8) | 80.7 (71.2, 89.8) | ||||||
| Phase 2 only (IgM/IgG) | IFA | 84.5 (54.4, 98.7) | 94.4 (79.8, 99.5) | 41.4 (26.0, 63.7) | 0.00 (0.00, 1.30) | 71.4 (62.2, 79.1) | 0.30 (0.16, 0.46) | 0.43 (0.24, 0.58) |
| CFT | 29.8 (17.0, 44.8) | 96.8 (89.2, 99.5) |
a
IFA, immunofluorescence assay; PI, predictive interval; PABAK, prevalence- and bias-adjusted K; modELISA, modified IDEXX ELISA. Prevalence 1 data represent estimated animal-level true prevalences in samples from a known infected herd. Prevalence 2 data represent estimated animal-level true prevalences in samples from New Zealand. Agreement data represent proportions of agreement. K data represent Cohen's kappa values.
b
Data represent estimates and include results from negative controls from New Zealand (declared C. burnetii-free by the OIE).