Influenza A and B virus IgG and IgM serology by enzyme immunoassays

Enzyme immunoassays (EIA) for IgG and IgM antibodies against influenza A and B virus are described. One hundred and seven subjects with a clinical diagnosis of acute respiratory infection (influenza, bronchitis or pneumonia) were selected for this study during two epidemics of influenza A which occurred in Finland in 1983 and 1985. Paired sera and nasopharyngeal secretions were obtained from all subjects. The sera were tested for influenza A and B antibodies by IgG and IgM EIAs and by complement fixation tests. The nasopharyngeal secretions were tested by an indirect EIA for influenza A and B antigens. The IgG EIA was found to be better than complement fixation for the diagnosis of influenza A infections: only 22% of the significant increases detected by this test were also positive by complement fixation. The additional contribution of the IgM EIA to the number of positives was minimal. It was also found that testing a single 1/1000 dilution of serum for influenza A and 1/100 dilution for influenza B in the IgG EIA gave as many positives as the conventional method of testing several dilutions.