the efficacy of residual chlorine content on the control of legionella spp. in hospital water systems.

outbreaks of legionellosis may be a side effect of institution-water treatment. however, the long-term outcomes and the predictive factors of legionella prevalence in such systems have still not been fully studied. this study was therefore conducted to investigate the prevalence of legionella spp. and to evaluate the role of bacteriological water quality parameters on its prevalence and removal in hospital water systems.a total of 45 samples were collected from distinct sites at seven hospitals in tehran, iran. the prevalence of this bacterium was assayed through a sensitive and specific technique for dna detection using pcr. multivariable stepwise regression analysis was used to explore the independent effects of the baseline factors on the incidence of legionella. two positive samples were also identified for species by dna sequencing.legionella were detected in 31.1% of samples. showerheads and cold-water taps were the most and the least contaminated sources with 55.3 and 9 percent positive samples, respectively. total mean of residual chlorine was 0.38 mg/l, with the peak value of 1.7 mg/l. legionella detection was proportional to the residual chlorine content of water and the results indicated that residual chlorine content is a critical factor in the incidence and proliferation of legionella (r=-0.33). the prevalence of legionella also coincided with the prevalence of hpc and amoeba cysts.the high positive rate of legionella colonization shows that hospital-acquired legionellosis might be under diagnosed in studied hospitals. further, legionella colonization is independent of the type of water, system characteristics and of preventive maintenance measures.