LEGIONELLA - World Health Organization

The rates (per number of tourists) of infection among travellers vary with the country visited.
In the period 1997–2002, using the United Kingdom international passenger survey statistics,
Turkey was reported as the country with the highest incidence rate, with 10–20 cases per
million travellers. Spain, Italy, Greece and France had incidence rates of between one and
seven per million travellers (EWGLI, 1999, 2001, 2004ab). Taken together, the countries in
southern Europe show higher incidence than those in the north. However, there is a trend
towards more declared cases being associated with travel within the home country — in 42%
of all the reported travel-associated cases in 1999, infection was related to travel within the
country of residence (Joseph, 2002b).
There may be important regional variations within countries (Cano et al., 1999) and also
among hotels. Cases of recurrent colonization in hotels have been known for some time (Bartlett
et al., 1984). In certain geographical areas (e.g. Benidorm, Spain), a significant percentage of
cases have been associated with a small number of hotels (Crespi et al., 1999). Analysis of the
data held on the EWGLI database indicated that a hotel previously associated with a case is
15% more likely to have another case than a hotel that has not had a case in the past (Slaymaker,
Joseph & Bartlett, 1999). In Spain, of 34 hotels associated with clusters in the period from
1980 to 1999, more than one third (13 hotels) had repeated cases or clusters of cases of Legionella
on two or more occasions (Martin, Pelaz & Baladrón, 2000).
These data suggest that infections from Legionella in hotels are not distributed at random,
and that certain hotels tend to transmit Legionella persistently. This can sometimes be attributed
to a relaxation of controls put into place after an initial outbreak, but in other cases the factors
contributing to continuing transmission are unknown.
Hot and cold-water systems — risk factors
Most information about the source of legionellosis in hotels has been obtained from outbreak
investigations, which show that the most common source of infection in hotels is the water
distribution system, particularly the hot-water system. In Spain, the vast majority of hotel
outbreaks in which the source of infection was determined microbially (by showing that
clinical and environmental isolates were related) were associated with water distribution systems.
In addition, in 12 out of 14 hotels that had subsequent cases after a first outbreak, the origin of the
infection was shown to be the hot-water system specifically (Martin, Pelaz & Baladrón, 2000).
The piped water systems of hotels and other tourist accommodation such as apartment hotels
are particularly susceptible to colonization by legionellae, because they have large, complex water
systems with a high surface-to-volume ratio, and may be subject to seasonal use with long
periods of low usage or stagnation. In addition, staff turnover may be high, making it difficult
to maintain training and competence.
Legionellae have been isolated from hotel water distribution systems throughout the world.
A study of hotels in five European countries (Austria, Spain, Germany, Italy and the United
Kingdom) found an average colonization rate of 55%, ranging from 33% in the United
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS