LEGIONELLA - World Health Organization

• Health-care facilities — Chapter 6 focuses on nosocomial cases of Legionnaires’ disease,
which tend to have a high case–fatality rate (the mortality rate can be as high as 40%),
although they comprise a smaller proportion of reported cases of legionellosis than communityacquired
cases. Underlying disease is a major risk factor for acquiring Legionnaires’
disease. Initially, cooling towers were thought to be the main source of legionellae in
health-care facilities, but many cases have been associated with piped hot and cold-water
distribution systems. Maintenance of temperatures outside the 20–50 °C range in the
network is the best way to prevent colonization of Legionella in distribution systems.
• Hotels and ships — Chapter 7 considers piped water systems of hotels, which are particularly
susceptible to colonization by legionellae because of their large size, their complexity and
their seasonal use patterns (which mean they may have long periods of stagnation and low
use). Preventive and control measures follow the same procedures identified for other
buildings; for example, they involve removing dead and blind ends, maintaining elevated
temperatures in the hot-water system, and periodic disinfection and permanent chlorination
of the cold-water system.
Chapter 7 also covers ships, which, like hotels, have complex water systems, and are difficult
to link to outbreaks or cases because passengers have usually dispersed before developing
symptoms. Ships also present particular challenges, as they are closed environments that
may increase the opportunity for transmission of airborne infection. Hot and cold-water
systems and spa pools have been implicated in a number of outbreaks of Legionnaires’
disease on ships.
• Natural spas, hot tubs and swimming pools — Chapter 8 covers these devices. Although there
are no recorded outbreaks of Legionnaires’ disease associated with bathing in swimming
pools, there is a risk of legionellosis from showers in the vicinity of pools, and these
should be managed as for hot and cold distribution systems in public buildings.
Thermal water systems, including hot tubs and display spas, have been responsible for
large outbreaks of Legionnaires’ disease. Hot tubs are a particular risk, due to the warm
water temperature (optimal for the growth of legionellae), high bather density, conditions
that increase the risk of nutrients for bacterial growth, areas of pipework that do not
receive disinfection from the pool water or hold stagnant water, and the potential to
inhale aerosols at a short distance from the water surface. Design, installation, management
and maintenance of these water systems must be undertaken with control of microbial
growth in mind. Disinfection, cleaning, monitoring and regular service and maintenance
are key factors in controlling Legionella.
Chapter 9 focuses on surveillance for Legionnaires’ disease, which is now a statutory notifiable
disease in most industrialized countries. National surveillance depends on the country’s
infrastructure and public health laws, and on surveillance principles and procedures. Because
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS xx