| OjectiveThis article is aimed to understand the relation between the quality of cooling water in central air conditioning and legionella pneumophila contamination, analyze the status of the quality of cooling water in central air conditioning and legionella pneumophila contamination, discover main risk factors of the quality of legionella pneumophila contamination in central air conditioning cooling water and provide theoretical basis for further protective measures and ensure people's safety.MethodThe study of cooling water in central air conditioning was conducted among 250 public places in Nanjing, Changzhou and Suzhou city in Jiangsu province and Shanghai city between 2008 and 2009. Cooling water indicators were collected for laboratory testing such as water temperature, pH value, conductivity, residual chlorine, turbidity, total dissolved solids, total bacteria, algae. And the environmental indicators were also measured such as air temperature, humidity, intensity of sunshine and intensity of UV. Descriptive statistics and Chi-square testing were carried out to analyze the status of central air conditioning cooling water in these cities. Correlation analysis, univariate and multivariate logistic regression analysis were applied to find out the risk factors of legionella pneumophila contamination in cooling water.Results1.2425 results were collected in this study. The statistical result of Kruskal-Wallis showed that the results among four cities had significant deviation.2. Among 243 legionella pneumophila results,187 samples were positive, the positive rate was 77%. The positive rate among four cities had significant deviation. The positive rate among three types of public places had no significant deviation.3. The analysis among the positive rate of legionella pneumophila in cooling water of different factors showed that:the value of chi-squire of positive rate in cooling water of different residual chlorine, turbidity were 22.8209,12.1301, and the value of P were 0.0001, 0.0070. The deviation had statistical significance.4. The risk factors of cooling water contaminated with legionella pneumophila in four city were water temperature and residual chlorine levels, and the regression equation was:logit (P)= 0.8705+0.8460Xwater temperature-0.6953Xresidual chlorine·The emergence of legionella pneumophila in cooling water where the temperature was above 30 and below 35.3℃was 2.33 times higher than that above 18 and below 30℃, the residual chlorine in cooling water higher than 0.05 and less than 2.2 mg/L was 0.499 times higher than the range between 0 and 0.05mg/L.5. The risk factors of legionella pneumophila contamination in Nanjing city was water temperature, and the regression equation was:logit(P)=2.1247+1.45X1, which means the odds ratio of legionella pneumophila positive rate when the water temperature was above 30 and below 35℃was 4.263 times higher than that above 23.8 and below 30℃.6. The risk factors of legionella pneumophila contamination in Shanghai city was conductivity and turbidity, and the regression equation was: logit(P)=-0.4350+1.2556X3+1.5335X5, which means the odds ratio of legionella pneumophila positive rate when the conductivity rate was higher than 4300 and lower than 4300 was 7.085. The odds ratio between turbidity greater than 5.0 NTU and lower than 5.0NTU was 4.452.ConclusionAt present, legionella pneumophila contamination in central air conditioning cooling water system was serious in China. Water temperature and residual chlorine are the pivotal factor influencing the growth and reproduction. So different responses and management measures in accordance with different characteristics and local conditions should be taken, and real-time monitoring of cooling water should also be strengthened. |
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