Sensitivity and specificity of enzyme immunoassay for serodiagnosis of influenza A virus infections.

Antibodies to influenza virus in sera from 40 patients infected with influenza A/USSR/90/77H1N1-like virus were measured by an enzyme immunoassay (EIA), and results were compared with those obtained by complement-fixation (CF) and hemagglutination-inhibition (HAI) tests. The sensitivity of EIA in detecting an increase in influenza antibody in sera from these 40 patients was intermediate (27 of 40) between the CF test (19 of 40) and the HAI test (35 of 40) when an ether-treater influenza A/USSR/77 virus was used as antigen in all three tests. In contrast with results from HAI tests, however, EIA did not reliably distinguish between infections caused by H1N1 and H3N2 viruses; EIA was thus most comparable in specificity to the CF test. It appears, therefore, that both EIA and CF tests measure antibodies directed to internal antigens common to all type A influenza strains, and that EIA with whole or ether-split influenza virus antigen may be a feasible alternative to the CF test for the type-specific serodiagnosis of influenza infections.