Flu@home: the Comparative Accuracy of an At-Home Influenza Rapid Diagnostic Test Using a Prepositioned Test Kit, Mobile App, Mail-in Reference Sample, and Symptom-Based Testing Trigger

Abstract

At-home testing with rapid diagnostic tests (RDTs) for respiratory viruses could facilitate early diagnosis, guide patient care, and prevent transmission. Such RDTs are best used near the onset of illness when viral load is highest and clinical action will be most impactful, which may be achieved by at-home testing. We evaluated the diagnostic accuracy of the QuickVue Influenza A+B RDT in an at-home setting. A convenience sample of 5,229 individuals who were engaged with an on-line health research platform were prospectively recruited throughout the United States. "Flu@home" test kits containing a QuickVue RDT and reference sample collection and shipping materials were prepositioned with participants at the beginning of the study. Participants responded to daily symptom surveys. If they reported experiencing cough along with aches, fever, chills, and/or sweats, they used their flu@home kit following instructions on a mobile app and indicated what lines they saw on the RDT. Of the 976 participants who met criteria to use their self-collection kit and completed study procedures, 202 (20.7%) were positive for influenza by qPCR. The RDT had a sensitivity of 28% (95% CI = 21 to 36) and specificity of 99% (98 to 99) for influenza A, and 32% (95% CI = 20 to 46) and 99% (95% CI = 98 to 99), for influenza B. Our results support the concept of app-supported, prepositioned at-home RDT kits using symptom-based triggers, although it cannot be recommended with the RDT used in this study. Further research is needed to determine ways to improve the accuracy and utility of home-based testing for influenza.

Keywords: RDT; SARS-CoV-2; antigen test; at-home testing; comparative accuracy; diagnostic accuracy; diagnostic performance; influenza; rapid tests; respiratory viruses.

FIG 1

Participant flow.

FIG 2

Flu positivity and Ct trends for trigger-test and onset-test intervals. Ribbons indicate 95% confidence intervals for fitted lines. (A) Flu positivity rates decreased as the time between triggering the flu@home kit and using the RDT increased. Though samples were small for longer intervals, there was a linear relationship between Ct and trigger-test interval (P < 0.001). B) Time intervals between participant-reported onset of first symptoms and using the RDT were distributed more widely than trigger-test intervals, but positive tests are still concentrated within the first 72 h to 96 h. There was a linear relationship between onset-test intervals and Ct values (P < 0.001).

FIG 3

Reference sample Ct trends and proportion of flu positives for number of symptoms and impact of illness on daily activities. (A) Ct values were inversely related to number of self-reported symptoms (P < 0.001) and participants with the most symptoms had a higher proportion of positive influenza cases (χ² = 28.15, P < 0.001). (B) Participants reported how much their illness impacted their ability to complete their daily activities. Ct values were negatively correlated with reported impact on activities (r_s = 0.22, P = 0.002) and there was a significantly greater proportion of influenza positive cases in the group reporting that their illness “very much” impacted their daily activities (χ² = 89.8, P < 0.001).