Using latent class analysis to estimate the test characteristics of the interferon-γ test, the single intradermal comparative tuberculin test and a multiplex immunoassay under Irish conditions

Tracy Clegg (1) , Anthony Duignan (2) , Clare Whelan , Eamonn Gormley (1) , Margaret Good (2) , John Clarke , Nils Toft (3) , Simon J. More (1)

1 School of Agriculture
2 Department of Agriculture and Food
3 Department of Large Animal Sciences

Considerable effort has been devoted to improving the existing diagnostic tests for bovine tuberculosis (single intradermal comparative tuberculin test [SICTT] and γ-interferon assay [γ-IFN]) and to develop new tests. Previously, the diagnostic characteristics (sensitivity, specificity) have been estimated in populations with defined infection status. However, these approaches can be problematic as there may be few herds in Ireland where freedom from infection is guaranteed. We used latent class models to estimate the diagnostic characteristics of existing (SICTT and γ-IFN) and new (multiplex immunoassay [Enferplex-TB]) diagnostic tests under Irish field conditions where true disease status was unknown. The study population consisted of herds recruited in areas with no known TB problems (2,197 animals) and herds experiencing a confirmed TB breakdown (2,740 animals). A Bayesian model was developed, allowing for dependence between SICTT and γ-IFN, while assuming independence from the Enferplex-TB test. Different test interpretations were used for the analysis: SICTT (standard and severe interpretation), γ-IFN (a single interpretation), and a range of interpretations for the Enferplex-TB (level-1 [high sensitivity interpretation] to level-5 [high specificity interpretation]). The sensitivity and specificity (95% posterior credibility intervals; 95% PCI) of SICTT[standard] relative to Enferplex-TB[level-1] and γ-IFN were 52.9-60.8% and 99.2-99.8%, respectively. Equivalent estimates for γ-IFN relative to Enferplex-TB[level-1] and SICTT were 63.1-70.1% and 86.8-89.4%, respectively. Sensitivity of Enferplex-TB[level-1] (95% PCI: 64.8-71.9%) was superior to the SICTT[standard], and specificity of the Enferplex-TB[level-5] was superior to γ-IFN (95% PCI: 99.6-100.0%). These results provide robust measures of sensitivity and specificity under field conditions in Ireland and suggest that the Enferplex-TB test has the potential to improve on current diagnostics for TB infection in cattle.

Mots clés: multiplex immunoassay.; Bovine tuberculosis; Ireland; latent class analysis; γ-interferon assay; single intradermal comparative tuberculin test; multiplex immunoassay

Domaines: Médecine vétérinaire et santé animale

Tracy Clegg, Anthony Duignan, Clare Whelan, Eamonn Gormley, Margaret Good, et al.. Using latent class analysis to estimate the test characteristics of the interferon-γ test, the single intradermal comparative tuberculin test and a multiplex immunoassay under Irish conditions. Veterinary Microbiology, 2011, 151 (1-2), pp.68. ⟨10.1016/j.vetmic.2011.02.027⟩. ⟨hal-00701909⟩