Legionella Infection Risk From Domestic Hot Water

Paola Borella; M. Teresa Montagna; Vincenzo Romano-Spica; Serena Stampi; Giovanna Stancanelli; Maria Triassi; Rachele Neglia; Isabella Marchesi; Guglielmina Fantuzzi; Daniela Tatò; Christian Napoli; Gianluigi Quaranta; Patrizia Laurenti; Erica Leoni; Giovanna De Luca; Cristina Ossi; Matteo Moro; Gabriella Ribera D'Alcalà


Emerging Infectious Diseases. 2004;10(3) 

In This Article

Abstract and Introduction

We investigated Legionella and Pseudomonas contamination of hot water in a cross-sectional multicentric survey in Italy. Chemical parameters (hardness, free chlorine, and trace elements) were determined. Legionella spp. were detected in 33 (22.6%) and Pseudomonas spp. in 56 (38.4%) of 146 samples. Some factors associated with Legionella contamination were heater type, tank distance and capacity, water plant age, and mineral content. Pseudomonas presence was influenced by water source, hardness, free chlorine, and temperature. Legionella contamination was associated with a centralized heater, distance from the heater point >10 m, and a water plant >10 years old. Furthermore, zinc levels of <20 µg/L and copper levels of >50 µg/L appeared to be protective against Legionella colonization. Legionella species and serogroups were differently distributed according to heater type, water temperature, and free chlorine, suggesting that Legionella strains may have a different sensibility and resistance to environmental factors and different ecologic niches.

Legionnaires' disease is normally acquired by inhalation or aspiration of legionellae from a contaminated environmental source. The first evidence of the association between potable water from shower and nosocomial legionellosis was reported approximately 20 years ago,[1] and the hot water system is thought to be the most frequent source of cases or outbreaks within a hospital,[2,3] where patients may be at a higher risk for a severe infection.[4,5,6] Relatively little is known about sporadically occurring cases of community-acquired legionellosis, which accounts for most infections,[7,8] although correlation analyses suggest that a substantial proportion of these cases may be residentially acquired and associated with bacteria in hot water distribution systems.[9]

Legionella spp. have been isolated from water with a temperature as high as 63°C, and the contamination is associated with other bacteria and protozoa.[10,11] Biofilm formation can provide a means for survival and dissemination of L. pneumophila,[12,13] interfering with efforts to eradicate bacteria from water systems.[14,15] The accumulation of microorganisms on the pipeline surfaces and the formation of biofilms are influenced by many factors, such as surface materials, concentration and quality of nutrients and disinfectants, temperature and hydraulics of the system, and pipe surface roughness.[16]

To assess the potential public health impact of Legionella colonization at a domestic level, a descriptive multicentric study was undertaken to identify and quantify the levels of the microorganism in a substantial number of Italian domestic hot water samples. Pseudomonas spp. are part of the natural population of the water, but some species should be considered as opportunistic pathogens. Furthermore, Pseudomonas may compete with Legionella to grow in the aquatic environment;[17,18] thus we also evaluated Pseudomonas colonization.

We addressed three specific aims: 1) to estimate the frequency of Legionella colonization and severity of contamination at the domestic level; 2) to identify potential risk factors for contamination relative to distribution systems and water characteristics; 3) and to define the relative role of each risk factor and suggest possible remediation. Lastly, risk for legionellosis was retrospectively evaluated by collecting information about pneumonia symptoms recorded by residents at home.