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)."
Guidelines for Drinking-water Quality
- source: World
Guidelines for Drinking-water Quality, World Health Organization
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
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."
plumbing systems can cause stagnation of water and provide a
suitable environment for the proliferation of Legionella."
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."
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."
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
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."
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."
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."
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,
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."