Abstract
The quantitative microbial risk assessment (QMRA) framework is used for assessing health risk coming from pathogens in the environment. In this paper, we used QMRA to evaluate the infection risk of L. pneumophila attributable to sink usage in a toilet cabin on Italian long-distance public transportation (LDT). LDT has water distribution systems with risk points for Legionella proliferation, as well as premise plumbing for drinking water, but they are not considered for risk assessment. Monitoring data revealed that approximately 55% of water samples (217/398) were positive for L. pneumophila, and the most frequently isolated was L. pneumophila sg1 (64%, 139/217); therefore, such data were fitted to the best probability distribution function to be used as a stochastic variable in the QMRA model. Then, a sink-specific aerosolization ratio was applied to calculate the inhaled dose, also considering inhalation rate and exposure time, which were used as stochastic parameters based on literature data. At L. pneumophila sg1 concentration ≤100 CFU/L, health risk was approximately 1 infection per 1 million exposures, with an increase of up to 5 infections per 10,000 exposures when the concentrations were ≥10,000 CFU/L. Our QMRA results showed a low Legionella infection risk from faucets on LDT; however, it deserves consideration since LDT can be used by people highly susceptible for the development of a severe form of the disease, owing to their immunological status or other predisposing factors. Further investigations could also evaluate Legionella-laden aerosols from toilet flushing.
Highlights
[19,23], we considered the relationship between infection risk and L. pneumophila sg1 load in water collected from the faucets, we calculated the probability of infection for each concentration category (Figure 4)
A public health perspective, perspective, particular attention is dedicated to L. pneumophila sg 1 since it is is the the most most prevalent reported strain of Legionella in building water systems [35] that is currently the predominant serogroup in clinical isolates, accounting for approximately 85% of cases confirmed by culture worldwide [36–38]
This paper addressed a currently little-explored topic represented by the risk assessment of Legionella on longdistance public transportation (LDT), using monitoring data collected from sinks of toilet cabins
Summary
Built environments for residential, tourist accommodation, healthcare, and longdistance public transportation (LDT) are equipped with various types of water storage and distribution systems for hygienic purposes and safe removal of human waste [1]. Apart from their design, the moist engineered surfaces of pipes and water tanks can be sensitive to biofilm growth; they represent an ecological niche for environmental bacteria, which can behave as opportunistic pathogens, such as nontuberculous mycobacteria, Pseudomonas spp., and Legionella spp. Particular attention is dedicated to Legionella spp. since Legionella pneumophila is one of the main etiological agents of epidemic pneumonia associated with water systems throughout the world [4–6].
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