Serological diagnosis of avian influenza in poultry: is the haemagglutination inhibition test really the ‘gold standard’?

BACKGROUND The serological diagnosis of avian influenza (AI) can be performed using different methods, yet the haemagglutination inhibition (HI) test is considered the 'gold standard' for AI antibody subtyping. Although alternative diagnostic assays have been developed, in most cases, their accuracy has been evaluated in comparison with HI test results, whose performance for poultry has not been properly evaluated. OBJECTIVE The objective of this study was to estimate the diagnostic sensitivity (Se) and specificity (Sp) of the HI test and six other diagnostic assays for the detection of AI antibodies without assuming a gold standard. METHODS We applied a Bayesian version of latent class analysis to compare the results of multiple tests from different study settings reported in the literature. RESULTS The results showed that the HI test has nearly perfect accuracy (i.e. 98·8% sensitivity and 99·5% specificity). It performed well in both chickens and turkeys and yet was less accurate in experimentally infected poultry, compared to naturally infected. Blocking ELISA and the indirect immunofluorescence assay also performed very well. CONCLUSIONS Given its very high Se and Sp, the HI test may be effectively considered a gold standard. In the framework of LPAI surveillance, where large numbers of samples have to be processed, the blocking ELISA could be a valid alternative to the HI test, in that it is almost as sensitive and specific as the HI test yet quicker and easier to automate.