A comparison of diagnostic assays for the detection of type A swine influenza virus from nasal swabs and lungs

Nasal swabs and lung samples from pigs experimentally infected with H1N1 sw ine influenza virus (SIV) were examined for the presence of SIV by the indi rect fluorescent antibody assay, immunohistochemistry, cell culture virus i solation, egg inoculation, and 2 human enzyme immunoassays (membrane enzyme immunoassay, microwell enzyme immunoassay). Egg inoculation was considered to be the gold standard for assay evaluation. The 2 human enzyme immunoass ays (EIA) and egg inoculation agreed 100% for the prechallenge nasal swabs. Agreement on SIV identification in nasal swabs with egg inoculation follow ing challenge was considered to be good to excellent for membrane EIA (kapp a = 0.85) and microwell EIA (kappa = 0.86). Agreement on SIV identification in lung tissue with egg inoculation following challenge was good to excell ent for membrane EIA (kappa = 0.75), fair for microwell EIA, fluorescent an tibody, and cell culture virus isolation (kappa = 0.48, 0.64, 0.62, respect ively), and poor for immunohistochemistry (kappa = 0.36). No assay was 100% accurate, including the "gold standard," egg inoculation. In light of this information, it is important to consider clinical signs of disease and a t horough herd history in conjunction with diagnostic results to make a diagn osis of SIV infection.