The performance of a commercially available, rapid membrane enzyme immunoassay for influenza A and B virus detection was compared to that of viral culture in 4,092 respiratory specimens collected from patients presenting with respiratory symptoms during the 2002-2003 influenza season. The test's overall sensitivity was 43.83%, lower than previously reported but similar for detection of both influenza A and B viruses (42.98 versus 44.76%). However, specificity, 99.74%, was excellent for both influenza A and B viruses (99.82 versus 99.92%). These values make this test a very good confirmatory test when clinical suspicion is high, but a less accurate screening test for large populations.Influenza viruses are important causes of morbidity and mortality in individuals of all age groups, especially the elderly and patients with chronic disabilities (5, 15). Influenza virus testing is often a part of the evaluation of febrile respiratory illness in hospital settings, as well as in the practitioner's office and emergency and urgent care centers (1,5,8,10,16). The reference method is viral culture. However, since the results of viral culture may be delayed for days to weeks, most centers perform rapid testing for influenza virus by immunofluorescence assay or enzyme immunoassay (2-6). A rapid and correct diagnosis is essential to help clinicians with decisions regarding early antiviral treatment, need for additional testing, and cohorting of the patients. Rapid response teams investigating outbreaks of severe respiratory disease also may use rapid tests to help differentiate between infection with influenza virus, biological warfare agents, such as those that cause anthrax and smallpox (2,8), and other causes of epidemic respiratory illnesses, such as coronaviruses associated with severe acute respiratory syndrome (5, 12, 13). Currently, there are several commercially available rapid influenza virus test kits that can easily be performed in less than 30 min (2, 4, 6, 9). However, these tests have different methodologies and performance characteristics and may be expensive to perform in large numbers (Table 1). Furthermore, the performance of rapid influenza virus tests and their impact on patient care should be evaluated periodically not only by manufacturers, but also by physicians and laboratories who perform the tests in large numbers of patients, in real-world clinical settings (2,3,10,11,16).
MATERIALS AND METHODSThis study evaluated the performance of a relatively new rapid test for detec- Rapid tests were routinely performed by virology laboratory technicians according to the manufacturer's instructions, 24 h daily, 7 days a week, and results were reported within 2 h of specimen receipt. Briefly, the BD Directigen Flu AϩB test is a rapid membrane enzyme immunoassay test that involves extraction of influenza A or B viral antigens from the patient specimens. The extracted specimen is expelled through a filter assembly into each of two wells of a triangular plastic test device containing a membrane surface. Viral ant...