LEGIONELLA - World Health Organization

F gure 0. Types of Legionella cases n Europe, by year of onset
Proportion
100% 100
90
80%
80
70
60%
60
50
40%
40
30
20%
20
10
0%
0
1987
1988
1989
Source: Information obtained from the European Working Group for Legionella Infections (EWGLI) 23
The risk of infection after exposure to Legionella is difficult to assess and remains a matter of some debate.
Since Legionella is ubiquitous in both natural and human-made environments, it must be assumed that most
people are exposed frequently, at least to single organisms. Generally, there is either no reaction to such
exposure or an asymptomatic production of antibodies. Drinking-water from natural sources and from public
supplies may carry single organisms or Legionella-containing amoebae. However, other than in health-care
facilities, there are no reports of outbreaks or recurrent cases of disease following consumption or use of
drinking-water that has been kept cool and not subjected to prolonged periods of stagnation.
Although it is impossible to completely eradicate legionellosis, the risks could be reduced to
a tolerable minimum. For example, decontamination of colonized installations has effectively
interrupted outbreaks and prevented recurrences of sporadic cases. In two prospective studies
conducted in hospitals, the frequency with which L. pneumophila was isolated from patients
with pneumonia was reduced from 16.3% to 0.1% over a six-year period; similarly, the
frequency of isolation from patients who were immunocompromised was reduced from 76%
to 0.8% over a 10-year period (Grosserode et al., 1993; Junge-Mathys & Mathys, 1994). These
reductions were due to hyperchlorination to prevent nosocomial infections.
Design measures can also help to prevent further outbreaks. For example, after the 1999 outbreak
in the Netherlands (Den Boer et al., 2002), the Dutch government launched a plan to combat
Legionnaires’ disease, emphasizing the need for greater vigilance by general practitioners
(GPs) and community health services. The plans included a computerized rapid alert system
for GPs, measures to ensure that all GPs and hospital casualty departments are alerted within
24 hours of possible cases of Legionnaires’ disease, and stricter controls of public buildings using
23 http://www.ewgli.org/
1990
Single
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
Linked Clustered Number of clusters
2002
2003
Number of clusters
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS