Thermal comfort, ventilation and mosquito-borne disease risk in Zanzibar hospitals

This pilot study investigated how thermal discomfort and indoor CO2 accumulation in four newly constructed district hospitals on Unguja island, Zanzibar, may elevate the risk of mosquito-borne disease (MBD) transmission, as heat-stressed occupants opening windows and doors inadvertently create entry points for mosquitoes attracted to the accumulation of indoor CO2. Over a 48-day period, air temperature, humidity, CO2 levels and door-opening frequency were measured across ward, clinical and waiting spaces. Thermal comfort was assessed using the Predicted Percentage of Dissatisfied index and interviews. Most spaces failed to meet ASHRAE 55 thermal comfort recommendations, with ward areas performing worst. In wards, CO2 levels frequently exceeded 700 ppm. Increased door-opening was recorded in three wards during peak activity periods of Anopheles and Culex mosquitoes. Workshops with hospital users and specialists confirmed ventilation and heat as the primary drivers for windows and doors being left open. Air-conditioned spaces often had higher CO2 levels due to air recirculation. Simulations of simple window shading adaptations demonstrated a reduction in solar radiation. These findings have implications for the design and retrofitting of health care infrastructure across sub-Saharan Africa to meet projected population growth. PRACTICE RELEVANCE Hospital building design in tropical climates may inadvertently increase the risk of MBD transmission when poor thermal comfort drives occupants to open windows and doors, thus facilitating mosquito ingress. This study identifies aspects of hospital building design, including solar exposure, cross-ventilation, landscaping and fan placement that contribute to poor thermal conditions and elevated CO2 levels. Simulations indicate that passive design measures such as façade shading can meaningfully reduce solar heat gain. This has informed subsequent co-created design adaptations across the same hospitals. Air-conditioned spaces elevated CO2 levels as a result of recirculation of air to reduce energy consumption, which may heighten rather than reduce MBD transmission risk. For policymakers and funders, early integration of passive cooling and ventilation standards into health care infrastructure requirements could offer a cost-effective pathway to improving patient comfort, reducing disease transmission and lowering long-term operational costs. This is particularly relevant across sub-Saharan Africa, where millions of additional hospital beds are planned.