Quantitative microbial risk assessment of Legionella pneumophila in a drinking water distribution system: A case study

Background

Legionella pneumophila poses a significant health risk in hospital water systems. This study assessed the risk associated with Legionella contamination in a hospital drinking water system in Sari, Iran, over one year.

Methods

Water samples were collected seasonally from various hospital taps, including patient room showers and toilet faucets. Both cold and warm water sources were analyzed. Water quality parameters, including pH, chlorine levels, and temperature, were measured. Legionella spp. were isolated and enumerated using standard microbiological techniques, and species identification was confirmed via 16S rRNA gene sequencing. A Quantitative Microbial Risk Assessment (QMRA) model was employed to estimate the infection risk from shower and faucet use.

Results

Legionella counts were significantly higher in warm water samples and during the summer season. A positive correlation was observed between Legionella counts and water pH, whereas negative correlations were found with chlorine levels and water temperature. QMRA results indicated that the estimated annual infection risk exceeded the acceptable limits set by the World Health Organization (WHO) and the United States Environmental Protection Agency (USEPA), particularly during summer.

Conclusions

The findings suggest that existing water management practices may be inadequate for controlling Legionella growth and transmission. Seasonal variations significantly impact infection risk, emphasizing the need for improved monitoring and control strategies. However, limitations related to sampling methodology, geographic specificity, and dose-response modeling should be considered when interpreting the results.