Rapid influenza diagnostic test (RIDT) are designed to detect influenza A and B nucleoproteic antigens in respiratory specimens, with results expressed qualitatively as positive or negative in no more than 15 min. Many different FDAapproved tests are available; while some assays are capable of distinguishing between influenza A or B viruses, none can distinguish between pandemic and seasonal strains of influenza A [1••, 2••]. Compared to reference methods (i.e. RT-PCR and viral culture), they have low sensibility (10 % to 80 %) and high specificity (95 % to 100 %), and there is also great variability between the different commercially available kits [25] [26] [27] . Sensitivity appears to be somewhat lower for influenza B than that seen for influenza A [26] . Also, the reported sensitivity for rapid tests is higher for nasopharyngeal samples than for throat swabs [27] . There are two main factors that influence RIDT's negative predictive value. First, negative results obtained during periods of high viral activity in the community are more likely to be false negatives; alternatively, false positives, though much less frequent, are more likely during periods of less viral circulation. Second, respiratory samples collected within the first 48 to 72 h of symptom onset positively influence RIDT's sensitivity. For these reasons, when rapid tests are negative, confirmation by means of RT-PCR or viral culture should be considered [1••, 2••]. Compared to RT-PCR, the sensitivity of RIDTs for detecting novel influenza A (H1N1) was equal to or lower than the sensitivity to detect seasonal influenza viruses [29] [30] [31] [32] , so RIDT results need to be interpreted with caution when evaluating patients suspected of having pandemic H1N1 influenza A.