Geostatistics – a tool applied to the distribution of Legionella pneumophila in a hospital water system

Abstract

[b]Introduction.[/b] Legionnaires’ disease is normally acquired by inhalation of legionellae from a contaminated environmental source. Water systems of large buildings, such as hospitals, are often contaminated with legionellae and therefore represent a potential risk for the hospital population. The aim of this study was to evaluate the potential contamination of [i]Legionella pneumophila[/i] (LP) in a large hospital in Italy through georeferential statistical analysis to assess the possible sources of dispersion and, consequently, the risk of exposure for both health care staff and patients. [b]Materials and Method. [/b]LP serogroups 1 and 2–14 distribution was considered in the wards housed on two consecutive floors of the hospital building. On the basis of information provided by 53 bacteriological analysis, a ‘random’ grid of points was chosen and spatial geostatistics or [i]FAIk Kriging[/i] was applied and compared with the results of classical statistical analysis. [b]Results[/b]. Over 50% of the examined samples were positive for [i]Legionella pneumophila[/i]. LP 1 was isolated in 69% of samples from the ground floor and in 60% of sample from the first floor; LP 2–14 in 36% of sample from the ground floor and 24% from the first. The iso-estimation maps show clearly the most contaminated pipe and the difference in the diffusion of the different [i]L. pneumophila[/i] serogroups. [b]Conclusion.[/b] Experimental work has demonstrated that geostatistical methods applied to the microbiological analysis of water matrices allows a better modeling of the phenomenon under study, a greater potential for risk management and a greater choice of methods of prevention and environmental recovery to be put in place with respect to the classical statistical analysis.

Keywords

• Legionella pneumophila
• hospital
• water systems
• geostatistics
• Kriging