Evaluation of a rapid enzyme immunoassay for detection of influenza A virus among adult and elderly patients

: Directigen Flu A, an enzyme immunoassay membrane test for the detection of influenza A virus, was compared with serum hemagglutinine inhibition assay in adult and elderly patients. Throat specimens were collected by vigorous swabbing from febrile patients who were suspect for influenza by clinical symptoms and tested with Directigen Flu A. Serum samples were collected from the patients at onset of illness and two to eleven weeks later and tested for antibody titer to influenza A/H1N1, A/H3N2, and B. A total of 57 patients were involved in this study; 32 under 59 years of age and 25 over 60 years of age. Influenza was diagnosed in 42 patients by HI titer elevation (73.7%). Directigen Flu A was positive in 25 patients. Results of Directigen Flu A and HI test agreed in 40 patients. Sensitivity and specificity of Directigen Flu A were 59.5% (25/42) and 100% (15/15), respectively. There was no significant difference in sensitivity between the two age groups. These results indicate the potential usefulness of Directigen Flu A in the surveillance of influenza A infection in the geriatric population. Directigen Flu A gives results within 15 minutes without expensive equipment. Use of Directigen Flu permits the timely administration of antiviral therapy and infection control among hospitalized and institutionalized geriatric patients.