Sensitive enzyme immunoassay for the rapid diagnosis of influenza A virus infections in clinical specimens.

Samples of nasopharyngeal secretion (NPS) from 100 infants and small children admitted for acute respiratory disease during the period from January to March 1989 were examined for the presence of influenza A virus. All samples were tested by enzyme immunoassay (EIA), fluorescent antibody (FA) technique and by isolation in cell culture 3-6 h after they were obtained from the patients. Of 24 influenza strains found by isolation, 21 were detected by EIA and 19 were FA+. In comparison with virus isolation, EIA gave the following values: sensitivity 88%, specificity 100%, positive prognostic value (PPV) 100%, and negative prognostic value (NPV) 96%. A rabbit anti-influenza-A serum (A-13) was used as catching antibody and a monoclonal anti-influenza-A pool against NP protein was used as detector antibody in EIA. A-13 gave bands corresponding to influenza A core proteins (NP and M1) in Western blot (WB) studies when different H3N2 strains were employed as antigens. A-13 gave only a band corresponding to the NP protein when H1N1 strains were examined by WB. The detection level by EIA for both H3N2 and H1N1 strains precipitated by polyethylene glycol from tissue culture maintenance medium was 1-2 ng.