[Study on the pollution and influencing factors of legionella pneumophila in industrial circulating cooling tower].

Objective: To investigate the pollution status of legionella pneumophila of industrial circulating cooling towers, and explore the factors affecting the positive rate and quantity of legionella pneumophila, in order to provide data support for the risk assessment and hierarchical management of legionella pneumophila in workplaces. Methods: In February, May, August and October 2023, the cooling water samples were collected from a total of 20 industrial circulating cooling towers of 9 enterprises in an industrial park in Shanghai. The water temperature, free residual chlorine, total residual chlorine, turbidity, chroma, pH, conductivity, chemical oxygen consumption, iron content and total plate count in the water samples were detected. Meanwhile, the legionella pneumophila in the water samples were qualitatively and quantitatively analyzed, and the influence of water quality indexes on the positive rate and number of legionella pneumophila detected was analyzed by logistic regression and linear regression respectively. Results: The positive rates of legionella pneumophila in the first to fourth quarters of 20 industrial circulating cooling towers of 9 chemical enterprises were 35% (7/20), 45% (9/20), 45% (9/20), and 85% (17/20). The serotypes of legionella pneumophila detected in the cooling tower were mainly legionella pneumophila type 1 (95.2%, 40/42), and the number of legionella pneumophila ranged from 0.2 to 316.8 cfu/ml. Circulating cooling water temperature (OR=1.36, 95%CI: 1.12-1.64, P=0.001) and conductivity (OR=1.02, 95%CI: 1.00-1.03, P=0.026) were independent risk factors affecting the detection of legionella pneumophila. There was a positive correlation between chemical oxygen consumption and the detected amount of legionella pneumophila (β=8.08, P=0.002) . Conclusion: The positive rate of legionella pneumophila in industrial circulating cooling water system is high, and the detected quantity fluctuates greatly, which may have health risks, suggesting that it is necessary to pay attention to the water quality management such as water temperature, conductivity and chemical oxygen consumption of industrial circulating cooling water and the monitoring and control of legionella pneumophila.