LEGIONELLA - World Health Organization

6.4.1 Identify control measures
This section should be read in conjunction with Chapters 4 and 5, which provide control measures
for potable water, in-building systems, cooling towers and evaporative condensers. Control
measures must be implemented in evaporative condensers installed in or near hospitals. In
Britain, most cooling towers have been removed from hospitals following a major outbreak
of legionellosis in 1985 (J Lee, Health Protection Agency, UK personal communication, June
2005). Where high-risk patients are housed, additional precautions should be considered,
such as installation of high-efficiency particulate absorbing (HEPA) filters on the air inlet and
monitoring of both the cooling systems and patients. One of the most effective control measures
is to maintain a temperature outside the range of 25–50 °C in the network, as discussed in
Chapter 3, Section 3.3.2.
Hot and cold-water systems — control measures
The guidance given here relates to general hospital hot and cold-water systems. In high-risk
areas, such as transplant centres and intensive care units, water from the outlet should be free
of Legionella (no colonies detectable in 1 litre of water). If this cannot be achieved within the
system then point-of-use filters will be needed at the outlet. Ice should be made either from
water that has had Legionella removed by filtration, or from heat-sterilized water.
If there is only an isolated colonization of a distal site, it is possible to flush out Legionella from
the site (for example, from a water tap). In the case of a systemic colonization of the water
distribution system, even intensive flushing causes no sustained reduction of legionellae.
In one study mentioned above (Kool et al., 1998), the water system was extensively modified,
and no further cases were identified in the hospital in the following year. The authors concluded
that Legionella can colonize hospital potable water systems for long periods, resulting in an
ongoing risk for patients, especially those who are immunocompromised. In the investigated
hospital, nosocomial transmission possibly occurred for more than 17 years before it was finally
interrupted in 1996 by extensively modifying the water system as a substantive control measure.
Point-of-use filters may also be used to mitigate the risk of legionellae.
Analysis of hot and cold-water systems for Legionella is no substitute for control measures;
rather, it is a verification that control measures are working.
Respiratory apparatus and tubing — control measures
Water that is used to rinse and clean respiratory apparatus should be sterile.
Because of the seriousness of nosocomial Legionella infections and the availability of low-cost sterile
water (proven to be effective in reducing proliferation of legionellae), sterile water should be
used in high-risk equipment such as respiratory devices, to avoid exposing at-risk hospitalized
patients to hospital water. Sterile water should also be used for rinsing and cleaning humidifiers,
nebulizers and respiratory machines.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS