Background: Rapid diagnostic tests (RDT) for influenza used by individuals at home could potentially expand access to testing and reduce the impact of influenza on health systems. Improving access to testing could lead to earlier diagnosis following symptom onset, allowing more rapid interventions on those who test positive, including behavioral changes to minimize spread. However, the accuracy of RDTs for influenza has not been determined among self-testing populations.
Objective: To assess the accuracy of an influenza RDT conducted at home by lay users with acute respiratory illness (ARI), compared to a self-collected sample conducted by the same individual mailed to a laboratory for reference testing.
Methods: A comparative accuracy study of an at-home influenza RDT (Ellume, Brisbane, Qld, Australia) in a convenience sample of individuals experiencing ARI symptoms. Participants were enrolled in February and March 2020, from the greater Seattle region, Washington, USA. Participants were mailed the influenza RDT and reference sample collection materials, which they completed and returned for RT-qPCR influenza testing in a central laboratory. We explored the impact of age, influenza type, duration, and severity of symptoms on RDT accuracy, viral CT (cycle threshold), and a marker of human DNA (RNase P).
Results: 605 participants completed all study steps and were included in our analysis, of whom 87 (14.4%) tested positive for influenza by RT-qPCR (70 influenza A, 17 influenza B). The overall sensitivity and specificity of the RDT compared to the reference test were 61% (95% CI 50-71) and 95% (95% CI 93-97), respectively. Among individuals with symptom onset ≤72 hours, sensitivity was 63% (95% CI 48-76) and specificity was 94% (95% CI 91-97), while for those with duration > 72 hours, sensitivity and specificity were 58% (95% CI 41-74) and 96% (95%CI 93-98), respectively. Viral load on reference swabs was negatively correlated with symptom onset, while quantities of the endogenous marker gene RNase P did not differ between PCR positive/negative groups, age groups, or influenza subtypes. The RDT did not have higher sensitivity or specificity among those who reported more severe illness.
Conclusions: The sensitivity and specificity of the self-test was comparable to that of influenza RDTs used in clinical settings. False negative self-test results were more common when the test was used after 72 hours of symptom onset, but were not related to inadequate swab collection, or severity of illness. Deployment of home tests may provide a valuable tool to support management of influenza and other respiratory infections.