Implications of the COVID-19 trajectory for the evaluation of hand hygiene interventions: Secondary analysis of the Soapp trial

Hand hygiene behavior is crucial to counter the spread of infectious diseases. However, its adoption during the early stages of the Coronavirus disease (COVID-19) pandemic showed temporal fluctuations associated with the trajectory of the pandemic (e.g. new COVID-19 infections). Such associations can confound conclusions about the effectiveness of interventions aimed at promoting hand hygiene during a pandemic. In this study, we performed a secondary analysis of a dataset from the optimization phase of Soapp, an app to promote hand hygiene during the COVID-19 pandemic. We used a longitudinal study design to test whether the associations between the pandemic trajectory and hand hygiene behavior were still present one year after the outbreak (primary outcome) and whether they impacted conclusions about the effectiveness of Soapp (secondary outcome). Participants (N = 216) were randomized to different versions of Soapp and used an electronic diary to self-report their hand hygiene behavior multiple times during the study. We considered the following indicators of the COVID-19 pandemic from the country of Switzerland in the period between March and August 2021: total cases/deaths, increases in recent new cases/deaths, new cases/deaths, and number of administered doses of vaccine. Data were analyzed using a multilevel approach. Results suggested that there were no significant associations between hand hygiene and the indicators of the pandemic trajectory. However, models including total cases/deaths impacted the conclusions about Soapp's effectiveness. Implications from this study are that the development and evaluation of hand hygiene interventions during a pandemic context should account for the trajectory indicators to maximize their effectiveness and control for confounding effects.