Considering the subtype-specific assays separately, the best ELISA performances resulted in comparison with H1N1pdm HI test with 87.89% (95%CI:83.25-91.62) sensitivity, 46.65% (95%CI:43.09-50.23) specificity, 35.21% (95%CI:31.51-39.05) PPV and 92.11% (95%CI:88.99-94.58) NPV. The best concordance was shown with H3N2 HI assay (K=0.4601, 95%CI:0.4059-0.5144).Conclusion: One hypothesis for the higher ELISA positivity rate may be indicative of a seroconversion against another IAV strain, but the different target antibodies of the two tests might be also taken into account. The false negative sera may be due to an early immune response in some animals, not detectable by the commercial kit. Infact, as suggested by some authors, ELISA test may not identify positive animals at the early stage of infection effectively as the HI, particularly when the virus is introduced to a naive swine population. In conclusion, the ELISA performances need to be improved, but the commercial kit can be used in SIV infection serodiagnosis. However, caution may be used since the test could miss recently exposed animals.