Objective: Reverse transcriptase polymerase chain reaction (RT-PCR) is accepted as a reference test for the virologic diagnosis of influenza A (HIN1)pdm09 virus infection. Yet because of the high cost, the need for special infrastructure and experienced personnel these tests can only be used in specific laboratories. As an alternative, rapid antigen tests have been widely used in the diagnosis of influenza virus infection. The sensitivity and specificity of rapid antigen assays in the diagnosis of seasonal influenza are known to be variable. In 2009, after the emergence of influenza A (H1N1) pdm09 virus, reevaluation of performance of antigen tests has been needed. The aim of this study is to compare the antigen test with real-time RT-PCR in the diagnosis of influenza A (H1N1) pdm09 infection and to determine the sensitivity, specificity and predictive values of the test.

Material and Method: In this study, 68 nasopharyngeal aspirate samples collected from pediatric patients between November 2009 and January 2010 were tested with a rapid diagnostic antigen test for influenza A and a real- time RT-PCR assay which detects both influenza A/B and influenza A (H1N1) pdm09. Results were compared in order to determine the performance characteristics of the antigen assay.

Results: Rapid antigen test was positive in 26/68 (38.2%) of samples while 40 samples were positive for influenza A with influenza A/B RT-PCR assay and 41 were positive for influenza A (H1N1) pdm09. The sensitivity and the specificity of the rapid antigen test were 62.5% and 96.2% compared to influenza A/B RT- PCR and 63.4% and 100% compared to influenza A (H1N1) pdm09 RT-PCR assay. Positive predictive value of the antigen test was 100% and negative predictive value was 64.2% compared to influenza A (H1N1) pdm09 RT-PCR test.

Conclusion: This study showed that rapid antigen test could be helpful in the diagnosis of influenza virus A (H1N1) pdm 09 infection in pediatric patients during an epidemic. Nevertheless, because of its low sensitivity, negative results should be confirmed with RT-PCR.