LEGIONELLA - World Health Organization

disseminate Legionella into the lower respiratory tract are used (such as medical humidifiers,
inhalation devices and respiratory therapy equipment). Retirement homes should be considered
with health-care facilities, as people with predisposing risk factors are likely to live there; and
several cases of legionellosis have been reported among residents of retirement homes
(Campese & Decludt, 2002b).
Cooling towers were originally thought to be the main source of nosocomial legionellosis, after
the bacteria were isolated from a cooling tower near a hospital dealing with cases of Legionnaires’
disease (Dondero et al., 1980). For example, the world’s biggest outbreak of legionellosis (Murcia,
Spain in 2001 with 449 confirmed cases) was shown by epidemiological and microbiological
investigation to be associated with the air-conditioning cooling towers of a city hospital (Garcia-
Fulgueiras et al., 2002). However, many nosocomial cases have been associated with piped
hot and cold-water distribution systems (Sabrià & Yu, 2002); ice made with water containing
legionellae has also been incriminated as a source of infection in hospitals, when patients
have been given ice cubes to suck (Stout, Yu & Muraca, 1985).
Underlying disease is a major risk factor for acquiring Legionnaires’ disease. Since the major
mode of transmission is aspiration, patients with chronic lung disease or those who undergo
surgery requiring general anaesthesia are at greater risk. One of the highest incidence rates of
nosocomial Legionnaires’ disease was in a population of surgical head and neck cancer
patients. This group of people has a propensity for aspiration, as a result of their oral surgery
(Johnson et al., 1985). Nasogastric tubes have been linked to nosocomial legionellosis in several
studies, with microaspiration of contaminated water the presumed mode of entry (Blatt et al.,
1994; Venezia et al., 1994). It is unlikely that colonization of the oropharynx by L. pneumophila
leads to transmission (Bridge & Edelstein, 1983; Pedro-Botet et al., 2002).
Heart transplant patients have been shown to have a high incidence of Legionnaires’ disease
(Hofflin et al., 1987; Mathys et al., 1999), whereas bone marrow transplant patients have a low
incidence (Chow & Yu, 1998). Corticosteroid administration is an independent risk factor
(Carratala et al., 1994; Lepine et al., 1998).
For people with predisposing risk factors, there is not only a higher risk of infection but also
a higher case–fatality rate (up to 50%) than in other settings, as a consequence of their often
immunosuppressed or predisposing status (Yu, 2000). Paradoxically, patients with acquired
immunodeficiency syndrome (AIDS) appear not to be at increased risk for nosocomial
Legionnaires’ disease (Gutiérrez et al., 1995).
6.1.1 Surveillance data on nosocomial Legionnaires’ disease
Between 1980 and 2001, 4021 cases of Legionnaires’ disease in residents of England and
Wales, United Kingdom were reported to the Communicable Disease Surveillance Centre’s
National Surveillance Scheme — an average of 183 cases per year. Of the total number of
cases, 269 were linked to hospital-acquired infection (PHLS, 2002).
0 LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS