Presence of Legionella Pneumophila and environmental factors affecting its growth, in the water distribution system in Taleghani hospital, Tehran

Legionella is one of the leading causes of nosocomial diseases. This bacterium can reproduce and survive under different temperatures, pH, nutrients and oxygen; while hot water of distribution systems provides an ideal environment for its growths. This study was carried out to identify Legionella in water distribution systems of Taleghani Hospital and to assess environmental factors affecting its growth. In this descriptive-cross sectional study which was run in summer 2011, 32 samples of cold and hot water systems of Taleghani Hospital were obtained. Samples with 1 to 1.5 liters volume were gathered and immediately concentrated using 0.45 µ membrane filter systems. BCYE culture along with GVPC, CCVC, L-Cystein and pyrophosphate Ferric supplementaries were made according to the protocol. In order to eliminate interference of other bacteia, GVPC, CCVC, and acid care for inhibition of growth were used. Then the samples were cultured and the colonies were recognized using morphology and biochemical characteristics. From 32 samples, 11 were contaminated with Legionella (34%). The residual chlorine of samples were 0.4-1.4 (mean: 0.909 mg/L) and their pH were 4.5-8.2 (mean: 7.36). Most of the positive cases were reported from hot water samples and also samples with residual chlorine of less than 1 mg/L. The positive samples were reported mostly from men oncology ward, storage tanks and newborn ward. Data analysis showed that there are significant correlations between legionella pneumophila growth and temperature (OR=1.676, (1.08-2.599); p-value <0.02) and also residual chlorine ((OR= 0.006, (0.0005-0.703); p-value <0.035); while no correlation was seen between other variables such as turbidity and pH. ‍ In spite of the fact that the hospital uses treated water of urban distribution system, 34% of samples were contaminated with legionella pneumophila; most of them were found in samples with residual chlorine concentrations of less than 0.9 mg/L. This shows that Legionella pneumophila is resistant against antiseptic factors and hard conditions of the environment, since most of the positive cases were related to hot water samples.