Background and purpose: Water microelements can influence the growth and colonization of Legionella and infections associated with these bacteria. This research investigated Legionella contamination of water regarding microelements, alkalinity and hardness in selected hospitals of Tehran.

Materials and methods: Hundred-fifty samples with 4 L volume were collected from cold and warm water system in three selected hospitals in Tehran. After determining the residual chlorine, pH and temperature, the samples were transferred to laboratory for filtration. Legionella culture was performed in supplemented BCYE_a (approved as a gold standard technique for environmental samples). Legionella colonies were identified using biochemical and morphological tests. Microelements (Fe, Mn, Zn, Cu, Alk, and hardness) were determined by photometric method. Data was analyzed applying Kolmogorov-Smirnov, Mann-withny, Spearman’s rank correlations, univariate and multiple logistic regression tests in SPSS V.15.

Results: Significant differences were seen in mean concentrations of all the microelements in positive and negative test of Legionella (P<0.05) except Cu (P>0.05). Spearman correlation implied a significant positive correlation between Fe, Mn, Zn, Alk, and hardness concentrations and Legionella density (P<0.05). Logistic regressions revealed that Mn concentration had the highest influence on Legionella occurrence (OR: 3.3).

Conclusion: Chemical quality of water influences its rate of Legionella contamination. Due to high densities of contamination, routine examination for Legionella detection and specific internal disinfection system in hospitals are advised to eradicate these bacteria.