Patient-reported outcomes and home-based self-swabs for influenza-like illness events - Lessons learned from the DANFLU-2 HomeSwab PRO Study

Abstract
Background
Patient-reported outcomes (PRO) and self-swab studies may offer to improve monitoring of infectious diseases. The DANFLU-2 HomeSwab PRO study aimed to assess the practicality of self-administered swabs and digital PRO tracking to monitor influenza-like illness (ILI).
Methods
As part of a sub-study of the DANFLU-2 trial, participants were instructed to self-report ILI and quality of life (QoL) using the

Respiratory Intensity and Impact Questionnaire

(RiiQ) for 14 days following symptom onset. If symptomatic, a home-based self-swab was performed, registered via a web app, and mailed to a central center for PCR testing by the participant. Weekly compliance reminders were sent through a governmental electronic letter system.
Results
Overall, 1,976 DANFLU-2 participants were enrolled. During the study period, 208 participants (10.5%) filled out at least one RiiQ, among which 171 (82.2%) reported symptoms fulfilling the ILI case definition. Response rate for completing all 14 days of RiiQs following an ILI event was 85.7% [IQR: 64.3; 100]. In total, 51.4% required phone reminders due to a 48-hour non-response period within the 14 days, with a median of 1 [IQR: 1; 1] contact attempts per non-responding participant. Overall, 89.4% of participants with an ILI event reported having performed a self-swab within a median of 1 day [IQR: 0; 3] from ILI symptom onset. In total, 65.8% of swabs were correctly registered in the web app, and 96.5% of all swabs tested RNaseP positive. During the study, 36 participants (1.8%) withdrew from the study after a median of 59 days [IQR: 25; 108], primarily due to bother from weekly reminders. To reduce dropouts, the possibility of adjusting frequency of reminders was offered, with 40 participants (2.0%) opting to receive monthly reminders and 47 (2.4%) opting to receive no further reminders. The DANFLU-2 staff received 323 e-mails with participant queries about the study. Responses were given to 167 queries via e-mail and 156 via phone calls.
Conclusion
The study confirmed the feasibility of using home-based self-swabs and digital PRO tracking within influenza studies. While the approach proved viable, the findings also highlighted areas for improvement in participant engagement and data collection efficiency.