LEGIONELLA - World Health Organization

In the outbreak of Legionnaires’ disease in Philadelphia in 1976, 34 out of 182 patients (18.7%)
died (Fraser et al., 1977). Subsequently, average mortality has been confirmed to be about
15–20% of hospitalized cases (Edelstein & Meyer, 1984; Guerin, 1992; Roig & Rello, 2003).
In the USA, the case–fatality rate was recorded as up to 40% in nosocomial cases, compared
with 20% among people with community-acquired legionellosis (CDC, 1997a). More recent
data from the USA and Australia showed case–fatality rates of 14% for nosocomial infections
and 5–10% for community-acquired infections (Benin et al., 2002; Howden et al., 2003). In
Europe, the overall case–fatality rate is about 12%. 3
Early ascertainment is an important factor for patient survival. In the largest recorded
outbreak, which occurred in Murcia, Spain, there were 449 confirmed cases, but the case–
fatality rate was only 1% (Garcia-Fulgueiras et al., 2003). This low fatality rate was probably
due to the clinicians’ awareness of legionellosis risk, as well as recognition that survival and
recovery depend on timely intervention and the correct choice of antimicrobial therapy,
particularly in severe cases (Tkatch et al., 1998; Gacouin et al., 2002; Roig & Rello, 2003).
Advanced age and comorbidity are predictors of death by Legionnaires’ disease. One study
evaluated prognostic factors of severe Legionella pneumonia cases admitted to an intensive
care unit (el Ebiary et al., 1997). In that study, the only independent factor related to death
was an APACHE score greater than 15 at admission (APACHE — acute physiology and
chronic health evaluation — is an algorithm for predicting hospital mortality). Cunha (1998)
has also published a scoring system, based on clinical signs of Legionnaires’ disease and
laboratory abnormalities.
1.3 Treatment of Legionnaires’ disease
Diagnostic tests
Tests for Legionnaires’ disease should ideally be performed for all patients with pneumonia at
risk, including those who are seriously ill, whether or not they have clinical features suggesting
legionellosis. Tests for Legionnaires’ disease should also be performed for patients displaying
symptoms that do not match any other diagnosis, and particularly on ill patients who are
older than 40 years, immunosuppressed, or unresponsive to beta-lactam antibiotics, or who
might have been exposed to Legionella during an outbreak (Bartlett et al., 1998). Urine antigen
tests, and cultures of sputum or bronchoalveolar lavage (washing the bronchial tubes and alveoli
with repeated injections of water), are the most suitable clinical tests for Legionella. Chapter 11
discusses diagnostic laboratory tests for Legionella.
3 http://www.ewgli.org/
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS