Analysis of air contamination with microorganisms in indoor public swimming venues in Pudong New Area, Shanghai, 2025

Objective To investigate the levels of air contamination with microorganisms in indoor public swimming venues in Pudong New Area, Shanghai, and identify the influencing factors.

Methods From July to September 2025, a survey was conducted at 26 indoor public swimming venues in Pudong New Area, Shanghai. Five indicators were measured, including air temperature, relative humidity, total bacterial count, and total bacterial and fungal counts in the supply air of central air conditioning ventilation systems. The Mann-Whitney U test was used to compare the differences in microbial indicators between groups. Spearman's rank correlation analysis was employed to identify the influencing factors of microbial indicators.

Results The M(P₂₅, P₇₅) of the indoor air temperature, relative humidity, total air bacterial count, total bacterial count in the supply air, and total fungal count in the supply air of the 26 investigated indoor public swimming venues were 29.6 (29.4, 29.8) ℃, 70.7% (70.1%, 71.5%), 2.0 (1.0, 5.0)CFU/plate, 304.0 (156.5, 440.3)CFU/m³, and 218.5 (140.0, 328.5)CFU/m³, respectively. The total bacterial count (M=327.0 CFU/m³) and total fungal count (M=263.0 CFU/m³) in the supply air of dedicated swimming venues were higher than those of multi-functional swimming venues (M=191.5 CFU/m³, 192.5 CFU/m³) (Z=-2.92, -2.72; both P < 0.05). The total bacterial count in the supply air of children's swimming venues (M=561.0 CFU/m³) was higher than that of adult swimming venues (M=269.0 CFU/m³) (Z=-3.16, P < 0.01). The total bacterial count (M=439.0 CFU/m³) and total fungal count (M=269.0 CFU/m³) in the supply air of medium- and small-sized swimming venues were higher than those of large-sized swimming venues (M=230.0 CFU/m³, 198.0 CFU/m³) (Z=-4.08, -2.19; both P < 0.05). In terms of influencing factors, there was a negative correlation between the total air bacterial count and relative humidity (r_s=-0.223, P < 0.05), and a positive correlation between the total air bacterial count and the total bacterial count in the supply air (r_s=0.388, P < 0.01). Additionally, the total bacterial count in the supply air was positively correlated with air temperature and the total fungal count in the supply air (r_s=0.259, P < 0.05; r_s=0.420, P < 0.01).

Conclusion The supply air of central air conditioning ventilation systems may be one of the sources of bacteria in the air of indoor public swimming venues in Pudong New Area, Shanghai, in the summer of 2025. Dedicated swimming venues, children's swimming venues, and medium- and small-sized swimming venues have relatively high risks of air contamination with microorganisms.