Factors Influencing the Case-fatality Rate of Legionnaires' Disease

Setting: The extent of the public health problem posed by Legionnaires' disease (LD) is not always well- appreciated.

Objective: To determine the characteristics and factors associated with the case fatality rate (CFR) of LD in Catalonia, Spain.

Design: Confirmed cases of LD reported during 1993-2004 were studied. Age, sex, hospitalisation, the type of diagnostic confirmation test and the personal risk factors for LD of cases were collected. Comparative bivariate and multivariate analyses according to origin (community-acquired or nosocomial) and nature (sporadic or outbreaks) were performed.

Results: Of 1938 cases reported, 164 died (case-fatality rate [CFR] 8.5%). The CFR fell from 35% in 1993 to 5.6% in 2004, and was higher in sporadic than in outbreak-associated cases (10% vs. 4.7%) and in nosocomial than community-acquired cases (31.7% vs. 6.8%). In community-acquired cases, the CFR was associated with age >70 years (OR 3.42, 95%CI 2.02-5.79), cancer (OR 4.58, 95%CI 2.36-8.90) and diagnostic confirmation methods other than Legionella urinary antigen test. The CFR of nosocomial cases was not associated with any of these factors.

Conclusions: The CFR of LD fell during the study period due to the incorporation of new diagnostic techniques and improved detection of outbreaks.