An App-Based Intervention to Protect Home Care Workers From Heat-Related Health Risks: Protocol for a Randomized Controlled Trial

Climate change is intensifying the frequency and severity of heatwaves, posing growing risks for workers. Home care workers face heightened heat risks due to physically demanding tasks, rising patient needs, frequent travel, and limited access to cooling environments. This study aims to causally evaluate the effectiveness of an app-based intervention (REHEAT strategy) in reducing adverse effects of heatwaves among Swiss home care workers. This multicenter, unblinded, randomized controlled trial (RCT) will involve 350 home care workers from the regions of Northern and Southern Switzerland. Participants will be randomized (1:1) into intervention and control groups, stratified by sex, age group, and geographical location. The intervention group will use the REHEAT app from June to September 2025, while the control group will gain access only after summer 2025. Both groups will be monitored over the summer using a wrist-worn wearable device (smartwatch), online questionnaires, diaries and cognitive tests. The impact of the REHEAT intervention will be evaluated using an Intention-To-Treat (ITT) approach to provide reliable real-world effect estimates, supplemented by Local Average Treatment Effects (LATE) analyses to assess impact based on participant exposure and compliance levels. Primary outcomes include strain accumulation, cognitive performance, emotional distress, sleep, night recovery, and mental and physical health. Outcomes will be analyzed longitudinally with mixed-effects models, while LATE will be estimated using app usage as an instrumental variable in generalized linear mixed models. At the time of submission, recruitment had been successfully completed, with a total of 350 participants enrolled in accordance with the study protocol. The intervention and data collection phases are ongoing, and no outcome data have yet been accessed or analyzed. The findings will inform the development of occupational health interventions in response to heat-related stressors and support climate change adaptation policies for health sector workers.