Accuracy of rapid influenza diagnostic test and immunofluorescence assay compared to real time RT-PCR in children with influenza A(H1N1)pdm09 infection

Abstract

The influenza burden among children is underestimated. The aim of our study was to estimate the accuracy of the rapid influenza detection test (RIDT) BD Directigen™ EZ Flu A+B® and direct immunofluorescence assay (DFA) used among children with influenza-like illness (ILI) consulted in the ambulatory care clinic. A total of 150 patients were enrolled in the study. Inclusion criteria were: age less than 59 months, presentation of ILI according to the CDC (Centers for Disease Control and Prevention) definition (fever >37.8°C, cough and/or sore throat in the absence of another known cause of illness), duration of symptoms shorter than 96 hours. Two nasal swabs and one pharyngeal swab were obtained from patients and tested by RIDT, DFA and real time RT-PCR as the reference method. For influenza A (H1N1)pdm09 virus sensitivity of RIDT was 62.2% (95% CI 46.5-76.2%), specificity 97.1% (95% CI 91.8-99.4%), PPV 90.3% (95% CI 74.3-98%), NPV 85.7% (95% CI 78.1-91.5%), for DFA sensitivity was 60% (95% CI 51.9-63.2%), specificity 96% (95% CI 88.7-98.8%), PPV 93.1% (95% CI 80.5-98%), NPV 72.7% (95% CI 67.2-74.9%). Analysis of logistic regression revealed that the chance of receiving a true positive result of RIDT was twice as high when the test was conducted during the first 48 hours of symptoms (OR 0.40 vs OR 0.22). The accuracy of RIDT is comparable with DFA and both methods are very specific but moderately sensitive in diagnosis of influenza in young children. Both methods may be recommended for screening for influenza among children.