Evaluation of the QuickVue influenza A+B rapid diagnostic test in a community setting

Background: Rapid influenza diagnostic tests can be useful to facilitate optimal treatment of seasonal influenza, and in a pandemic scenario could potentially be important tools for control and mitigation as well as clinical management. We evaluated the performance of the QuickVue Influenza A+B test (Quidel Corp., San Diego, California) among a large community sample of patients presenting with influenza-like-illness in a sub-tropical setting. Methods: Patients older than 2 years whose chief complaint consisted of any combination of at least 2 influenza-like symptoms were recruited from 25 outpatient clinics in Hong Kong during the 2007 influenza season. Two sets of nasal and throat swabs were obtained using a standardized protocol from each patient. One set of swabs was combined and tested by QuickVue while the other was sent for viral culture (gold standard) by standard methods. Results: 946 subjects were enrolled, 11 of whom were excluded due to missing or contaminated laboratory samples. In the remaining 935 subjects, QuickVue had sensitivity 68% and specificity 96%, with positive predictive value 78% and negative predictive value 93%. Age stratification showed that the rapid test had lower sensitivity in adults aged 16 or above (67%) compared to children (73%); within children the sensitivity further increased with younger age (82% in under-5s). We also found higher sensitivity in subjects who were tested within 24 hours of symptom onset (69%) versus those tested 24-48 hours after onset (62%). Conclusions: Our findings suggest that QuickVue has slightly lower sensitivity in the community setting compared to most previous evaluations typically under more controlled conditions such as laboratories and hospitals. Our finding that sensitivity varies by age and time of symptom onset is likely explained by the greater degree of viral shedding in children and earlier in the course of illness