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Engagement with mHealth COVID-19 digital biomarker measurements in a longitudinal cohort study: a mixed methods evaluation.

BACKGROUND
The COVID-19 pandemic accelerated the interest in implementing mHealth in population-based health studies, but evidence is lacking on engagement and adherence in studies. We conducted a fully remote study for over 6-months tracking COVID-19 digital biomarkers and symptoms using a smartphone app nested within an existing cohort of UK adults.


OBJECTIVE
To investigate participant characteristics associated with initial and sustained engagement in digital biomarker collection from a bespoke smartphone app and if engagement changed over time or as a result of COVID-19 factors. To explore participants' reasons for consenting to the smartphone sub-study and experiences related to initial and continued engagement.


METHODS
Participants in the Fenland COVID-19 study were invited to the app sub-study from August-October 2020 until study closure (30 April 2021). Participants were asked to complete digital biomarker modules (oxygen saturation, body temperature, resting heart rate (RHR)) and possible COVID-19 symptoms in the app three times/week. Participants manually entered measurements, except RHR measured using the smartphone camera. Engagement was categorised from median weekly frequency of completing the three digital biomarker modules (categories; 0, 1-2 and 3 or more/times per week). Socio-demographic and health characteristics of those who did or did not consent to the sub-study, and by engagement category were explored. Semi-structured interviews were conducted with 35 participants and data analysed thematically; 22 who consented to the app sub-study and 13 who did not consent, purposively sampled by sex, age, educational attainment and by engagement category.


RESULTS
A total of 2,524 (63%) of Fenland COVID-19 study participants consented to the app sub-study. Of those, 90.2% completed the app onboarding process. Median time in the app sub-study was 34.5 weeks (IQR 34, 37) with no change in engagement from 0-3 months or 3-6 months. Completion rates (1/week) across the study between digital biomarkers were similar (RHR 72.8%, temperature 73.1%, oxygen saturation 73.5%). Older age groups, lower managerial and intermediate occupations were associated with higher engagement whilst working, being a current smoker, overweight or obese and high perceived stress were associated with lower engagement. Reasons for consenting included altruism, previous positive participation experiences and interest in health research, and non-consent was due to confusion regarding study invitation and perceived phone incompatibility. Continued engagement was facilitated by routine and personal motivation, poor engagement was caused by user error and app/equipment malfunctions preventing data input. From these results we developed key recommendations to improve engagement in population-based mHealth studies.


CONCLUSIONS
This mixed-method study demonstrated both high initial and sustained engagement in a large mHealth COVID-19 study over at least 6-month period in UK adults. Being nested in a known cohort study enabled the identification of participant characteristics and factors associated with engagement, to inform future applications in population-based health research.


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