Legionnaire's disease (LD) is a major cause of both community acquired and nosocomial pneumonia, with Legionella pneumophila serogroup A (Lp1) being the most virulent and the greatest cause of disease. Sample culture of low respiratory tract is considered the gold standard in the diagnosis of LD, however its sensitivity seems to be poor and its performance is technically demanding. The introduction of urinary antigen detection testing (LUA) brought a major advance in LD diagnosis, with upt to 95% of cases in Europe being diagnosed with this method. Despite the high sensitivity of LUA for Lp1, ranging from 80-90%, its negative predictive value is low in other serogroup than Lp1 and therefore, Legionella may be unrecognized as agent of pneumonia. Although underdiagnosed and underreported, LD represents the second most common cause of pneumonia requiring admission in intensive care unit (ICU). Average fatality rate of LD in Europe reaches 10%, but its mortality is considered to be even higher in nosocomial patients.

Despite the higher fatality rate in hospitalized LD patients, poor is the knowledge on the risk factors that could induce disease and that increase mortality in the hospitalized population affected by LD. In order to shed more light on this topic a cohort of patients diagnosed with LD in the last 3 years will be retrospectively examined.

Inclusion Criteria:

All confirmed human cases of Legionnaires' disease diagnosed within the CHU Brugmann hospital within the last 3 years, from 01/01/2016 till 31/12/2018. A similar approach will be followed for the St Pierre and the UZ Brussel Hospitals.

Exclusion Criteria:

Pregnant women.

All confirmed human cases of Legionnaires' disease diagnosed within the CHU Brugmann hospital, the St Pierre Hospital and the UZ Brussel Hospital. The definition of Legionnaires' disease diagnosis is met whether a seroconversion is detected or positive respiratory samples cultures are objectivized or positive LUA are observed. Seroconversion is defined as a rising of Legionella antibodies, dilution superior to 1/128 by indirect immunofluorescence. Nosocomial cases of Legionnaires' disease are defined in this study as the ones having an onset of symptoms more than 10 days after hospitalization.