Burden of heat stress on residual work capacity among farmers living with chronic HIV in Siaya county, Kenya: a longitudinal observational study protocol

Introduction: Sub-Saharan Africa, including Siaya County in Kenya, has a high prevalence of chronic HIV infection, which may increase vulnerability to climate-induced heat stress among agricultural workers. Understanding how HIV moderates the relationship between environmental heat exposure and labour capacity is essential for designing targeted, equitable public health interventions in climate-vulnerable settings. This study aims to quantify the effects of heat exposure on labour capacity and sleep, assess whether physiological strain mediates these effects, and examine whether HIV status and sex affect the observed relationships. Methods: This is an ongoing 24-month longitudinal observational study involving 124 participants (62 male-female pairs) stratified by HIV status. HIV-positive participants are recruited from the Wagai Health Centre's HIV clinic, and HIV-negative participants are recruited from the general population via the Siaya County Health and Demographic Surveillance System (HDSS) registry. The participants are aged 20-45 years and engaged in agricultural livelihoods. Environmental heat exposure (indoor and outdoor wet bulb globe temperature), actigraphy (physical activity and sleep), and physiological metrics (heart rate and core body temperature) are continuously or periodically monitored using research-grade wearables. GPS data and monthly questionnaires on thermal comfort, work timing, and heat-related symptoms are collected to contextualize physiological responses. Data collection occurs sequentially-first 12 months for the HIV-negative group and then another 12-months for the HIV-positive group-ensuring seasonal alignment across cohorts. Mixed-effects models will assess the associations between heat exposure and residual labour capacity (primary outcome) and sleep quality (secondary outcome), examining mediation by physiological strain and moderation by HIV status and sex. The models will be adjusted for age, body composition, and other potential confounders. Discussion: This study will generate novel evidence on the impact of heat stress on labour capacity and sleep in HIV-positive populations, addressing a critical gap in climate-health research in sub-Saharan Africa. Findings will inform equitable adaptation strategies, such as work-rest cycles and hydration protocols, tailored to vulnerable subgroups, including women and individuals living with HIV.