Association of indoor multiple airborne pollutants co-exposure and typical respiratory symptoms among gym employees: A nationwide observational study in China.

Gym employees are exposed to pollutants in indoor gyms, but evidence on the combined effects of multiple pollutants remains limited. This observational study examined the associations of co-exposure to PM2.5, PM10, total fungal count (TFC) and total plate count (TPC) with respiratory symptoms among employees in 280 gyms across 32 provinces of China (2022-2023) The median concentrations of PM2.5, PM10, TFC, and TPC were 35.00 μg/m3, 59.00 μg/m3, 170 CFU/m3, and 226 CFU/m3, respectively. 22.13% of employees self-reported respiratory symptoms. PM2.5 (OR = 2.31), PM10 (OR = 2.19), TFC (OR = 1.17), and TPC (OR = 1.24) were positively associated with respiratory symptoms (P < 0.05). Notably, the co-exposure to four pollutants was positively associated with respiratory symptoms using the Quantile g-computation model (OR = 1.70), with PM2.5 and TFC as the main components (P < 0.05). Protective factors included natural ventilation (OR = 0.36) and high-efficiency filters (OR = 0.42), whereas lack of equipment disinfection (OR = 3.30) and use of air-return air-conditioning systems (OR = 2.85) increased risk of respiratory symptoms (P < 0.05). Among four potential indices, including the Fuzzy Synthetic Index, Comprehensive Evaluation Index, I1 Index, and Indoor Air Quality Index, the I1 Index showed a consistent positive association with respiratory symptoms across all grades (OR 2.40-3.05, P < 0.05). Despite limitations inherent to the cross-sectional design and self-reported respiratory data, our findings provide nationwide evidence on the respiratory health of airborne pollutant co-exposure in gyms and underscore the role of integrated ventilation, air-conditioning maintenance, and hygiene management strategies for reducing respiratory symptoms among employees.