Background: The influenza virus is responsible for causing major respiratory tract symptoms. A fast, accurate diagnosis is essential for efficient treatment, especially in patients with complications. The Rapid Influenza Diagnostic Tests (RIDTs) for influenza detection have been developed to subtype the influenza virus. The re-evaluation of the rapid test is needed in terms of specificity, sensitivity, and accuracy.
Methods: From August 13, 2010 to September 22, 2011, 1,076 nasal aspirates were obtained from patients, ages ranging from 15 days to 98 years, with symptoms of influenza-like illness (ILI) and evaluated by 2 types of RIDTs, Standard Diagnosis (SD) and QuickVue (QV) Rapid tests followed by real-time RT-PCR. The results from the rapid test diagnoses were compared to those from real-time RT-PCR.
Results: During 2010 and 2011, the estimated sensitivity of the SD rapid test for seasonal H3, human pandemic H1N1, and influenza B infection was 49.4%, specificity was 84.1%, positive predictive value was 47.6%, and negative predictive value was 85% while those of the QV rapid test were 63.4%, 96.7%, 94.8%, and 80.3%, respectively. Infant patients (< or = 5 years) yielded less false negatives while adolescents and adults (older than 5 years) showed more false negatives 8.8% and 15.2%, respectively. Using rapid test diagnosis, H3N2 influenza virus was found with more false negative results (11.1%) than the other viruses (1.1 - 3.5%). The SD rapid test appeared to be more sensitive than the QV test during high season activity while the QV test was more sensitive during the period of low influenza virus activity.
Conclusions: Due to persistent genetic drift of the influenza virus, the available RIDTs should be re-evaluated each year. During 2010 - 2011, the QV rapid test showed more reliable results than the SD rapid test. However, the false negative results of H3N2 influenza virus detection during its peak should be cause for concern. Some of the results, e.g. patients with complications, should be compared with real-time RT-PCR as the gold standard method for detecting influenza virus infection.