Objectives To investigate the microbial contamination status of air conditioning system in public places in Shenzhen from 2014 to 2018.

Methods Hygienic investigation was carried out on the inner surface of air ducts and air supply systems as well as cooling water and condensed water of air conditioning systems in 117 public places in the city. Chi-square test was used to analyze the test result.

Results From 2014 to 2018, the test result of centralized air-conditioning and ventilation systems in 117 public places showed that:the qualified rates of total bacteria and fungus on the inner surface of air ducts were 93.8% and 93.3%, respectively; the qualified rates of total bacteria, total fungus, and β-hemolytic streptococcus in air supply systems were 72.0%, 80.6% and 98.6%, respectively; and the detection rates of Legionella pneumophila in cooling water and condensed water were 11.7% and 1.1%, respectively. The qualified rate of microorganism in air supply of air conditioner is lower than that on the inner surface of air ducts, and the detection rate of Legionella pneumophila in cooling water decreases year by year. There were statistically significant differences in the qualified rates of the total bacteria and total fungus on the inner surface of the air duct, the total fungus in the air supply of the air conditioner and Legionella pneumophila in the cooling water (χ² were 33.066, 102.314, 23.512, and 22.744 respectively, P < 0.05).

Conclusions In view of the microbial contamination of air-conditioning system in public places in the city, the monitoring of microorganisms in air-conditioning system should be strengthened, and the guidance of cleaning and disinfection of air-conditioning system and hygienic management of daily operation should be strengthened in business places.