"Since Legionella is a respiratory pathogen, systems that generate aerosols, such as cooling towers, whirlpool baths, and shower heads, are the more commonly implicated sources of infection, with the hot water supply system generally being the origin of the contamination. However, the cold water supply, when held within the range of Legionella multiplication (25°C), has also been implicated (Hoebe et al., 1998)."
source: Health Canada

Guidelines for Drinking-water Quality - source: World Health Organization

Legionella

Excerpt source: Guidelines for Drinking-water Quality, World Health Organization

• "The genus Legionella, a member of the family Legionellaceae, has at least 42 species. Legionellae are Gram-negative, rod-shaped, non-spore-forming bacteria that require L-cysteine for growth and primary isolation. Legionella spp. are heterotrophic bacteria found in a wide range of water environments and can proliferate at temperatures above 25 °C."

• "Legionella bacteria are ubiquitous in the environment and can proliferate at the higher temperatures experienced at times in piped drinking-water distribution systems and more commonly in hot and warm water distribution systems. Exposure to Legionella from drinking-water is through inhalation and can be controlled through the implementation of basic water quality management measures in buildings and through the maintenance of disinfection residuals throughout the piped distribution system."

• "Poorly designed plumbing systems can cause stagnation of water and provide a suitable environment for the proliferation of Legionella."

• "...relatively high amounts of biodegradable organic carbon, together with warm temperatures and low residual concentrations of chlorine, can permit growth of Legionella, V. cholerae, Naegleria fowleri, Acanthamoeba and nuisance organisms in some surface waters and during water distribution."

• "Legionella spp. are common waterborne organisms, and devices such as cooling towers, hot water systems and spas that utilize mains water have been associated with outbreaks of infection."

• "Owing to the prevalence of Legionella, the potential for ingress into drinking-water systems should be considered as a possibility, and control measures should be employed to reduce the likelihood of survival and multiplication."

• "Disinfection strategies designed to minimize biofilm growth and temperature control can minimize the potential risk from Legionella spp. The organisms are sensitive to disinfection. Monochloramine has been shown to be particularly effective, probably due to its stability and greater effectiveness against biofilms."

• "Water temperature is an important element of control strategies. Wherever possible, water temperatures should be kept outside the range of 25–50 °C. In hot water systems, storages should be maintained above 55 °C, and similar temperatures throughout associated pipework will prevent growth of the organism. However, maintaining temperatures of hot water above 50 °C may represent a scalding risk in young children, the elderly and other vulnerable groups."

• "Where temperatures in hot or cold water distribution systems cannot be maintained outside the range of 25–50 °C, greater attention to disinfection and strategies aimed at limiting development of biofilms are required."

• "Accumulation of sludge, scale, rust, algae or slime deposits in water distribution systems supports the growth of Legionella spp., as does stagnant water."

• "Systems that are kept clean and flowing are less likely to support excess growth of Legionella spp. Care should also be taken to select plumbing materials that do not support microbial growth and the development of biofilms."

• "...Legionella, atypical mycobacteria, Burkholderia pseudomallei and Naegleria fowleri are environmental organisms that can grow in water and soil. Besides ingestion, other routes of transmission can include inhalation, leading to infections of the respiratory tract (e.g., Legionella, atypical mycobacteria), and contact, leading to infections at sites as diverse as the skin and brain (e.g., Naegleria fowleri, Burkholderia pseudomallei)."

• "Although all Legionella spp. are considered potentially pathogenic for humans, L. pneumophila is the major waterborne pathogen responsible for legionellosis, of which two clinical forms are known: Legionnaires’ disease and Pontiac fever. The former is a pneumonic illness with an incubation period of 3–6 days. Host factors influence the likelihood of illness: males are more frequently affected than females, and most cases occur in the 40- to 70-year age group. Risk factors include smoking, alcohol abuse, cancer, diabetes, chronic respiratory or kidney disease and immunosuppression, as in transplant recipients. Pontiac fever is a milder, self-limiting disease with a high attack rate and an onset (5 h to 3 days) and symptoms similar to those of influenza: fever, headache, nausea, vomiting, aching muscles and coughing. Studies of seroprevalence of antibodies indicate that many infections are asymptomatic."