LEGIONELLA - World Health Organization

6.3.2 Assess hazards and prioritize risks
This step involves collecting and evaluating information on specific hazards associated with
health-care settings, and conditions leading to their presence, to decide which are significant
for safety and therefore should be addressed in a safety plan. The hazards considered here
include those associated with the system components listed in Table 6.2.
Hot and cold-water systems — risk factors
The risk of nosocomial Legionnaires’ disease associated with the colonization of hot and
cold-water systems by Legionella is well established. For example, Joly & Alary (1994) performed
a follow-up study for 9 months at 20 hospitals, and found that the 10 hospitals containing
readily detectable Legionella experienced significantly more frequent cases of Legionnaires’
disease than did the 10 hospitals where Legionella was not readily detected (P = 0.054).
A five-year prospective study in 20 hospitals in Spain analysed the incidence of new cases of
nosocomial legionellosis. In 64.7% of hospitals, Legionella-positive water cultures were found
and nosocomial legionellosis was diagnosed; however, in hospitals where Legionella was not
detected, no nosocomial legionellosis was reported. The reported incidence of nosocomial
legionellosis has increased significantly since environmental studies increased detection of the
organism (Sabrià et al., 2004).
The proportion of distal sites in the water system of a hospital that are positive for Legionella
directly correlates with the incidence of Legionnaires’ disease; that is, the greater the percentage
of sites holding Legionella, the more likely it is that cases will occur. The opposite is also true
— if Legionella is not detected in the water supply, cases will not occur (Stout & Yu, 2001).
Based on the evidence of a link between the colonization of hot and cold-water systems in
hospitals and other buildings and the risk of a Legionella infection, Exner et al. (1993) investigated
hospitals, residential units and other buildings that could be affected by the colonization of
water systems with Legionella. The study distinguished between:
• a local or non-systemic colonization (defined as a colonization of isolated parts of the system,
such as water outlets or shower heads)
• a systemic colonization of the water system (defined as a colonization of the whole system,
including the central parts of the water supply).
Table 6.3 shows the type of colonization of water distribution systems by Legionella in healthcare
facilities in Germany.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS