LEGIONELLA - World Health Organization

Kingdom to 66% in Spain (Starlinger & Tiefenbrunner, 1996). In Mallorca, Spain, of 114 hotel
water systems sampled, 45.6% were positive for Legionella (Crespi et al., 1999). A survey in
the United Kingdom of 103 hotels between 1982 and 1984 found that Legionella was present in
20% of hotels in the north, 43% in the midlands and 52% in the south (Bartlett et al., 1985).
These studies also show that the prevalence of Legionella in a water distribution system correlates
to a large degree with the water temperature — isolation rates are highest in warm water systems,
particularly within a temperature range of 25–50 °C. Starlinger & Tiefenbrunner (1996) also
showed a positive correlation between the presence of Legionella and amoebae in some installations.
Few published data are available on the concentrations of Legionella in the piped water systems
of hotels that are colonized but have not been associated with outbreaks. In Germany, Habicht
& Muller (1988) detected concentrations of 10 1 –10 3 CFU/ml in most of the samples analysed,
with a maximum of 10 5 CFU/ml.
Hot and cold-water systems on ships have also been implicated in a number of outbreaks.
Following an outbreak on a cruise ship in Italy in 1995 and 1996, strains of L. pneumophila
serogroup 1, identical by monoclonal subtyping and genomic fingerprinting, were isolated
from patients and the ship’s water supply, although the exact source of the infection was not
established (Pastoris et al., 1999). In 1998, an outbreak of Legionnaires’ disease occurred on a
cruise ship that sailed to the Mediterranean and the Norwegian fjords (Arthur, 1998). Water
samples taken from the hot-water system at shower heads were contaminated with legionellae.
The ship was unable to maintain safe temperatures in both hot and cold-water systems, and
the chlorine dosing system on board the ship was not working effectively (Arthur, 1998). In
June 2001, two mechanics working on a cargo ship under repair in Barcelona, Spain were reported
to have died after contracting Legionnaires’ disease. The mechanics had been working with
the pump of the ship’s water system. Molecularly indistinguishable isolates of L. pneumophila
serogroup 1 subgroup Pontiac (Knoxville) were isolated from one of the patients and from
the cooling water circuit valve of the ship’s pump (Cayla et al., 2001).
Hot tubs and recreational pools — risk factors
Hot tubs are installed on many cruise ships and on some ferries. The risks are similar to those
on land (see Chapter 8), and there have been several outbreaks on ships due to hot tubs. In
1994, a cruise ship had 50 cases of Legionnaires’ disease, spread over nine cruises. The disease
was believed to have been caused by inadequate bromination of the ship’s three hot tubs, and
the risk of acquiring Legionnaires’ disease increased by 64% for every hour spent in the hot
tub (Jernigan et al., 1996). Passengers spending time around the hot tub, but not in the
water, were also significantly more likely to have acquired infection. L. pneumophila serogroup 1
was isolated only from the sand filter of a hot tub (Jernigan et al., 1996).
In 1997, an outbreak occurred on a Rhine cruiser and affected six people. One man had fallen
into the cruiser’s hot tub and subsequently developed Legionnaires’ disease. Large numbers
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS