Risk factors for sporadic community-acquired Legionnaires' disease. A 3-year national case-control study

Risk factors for sporadic community-acquired Legionnaires' disease (LD) have been studied in the past, well before the widespread introduction of the urinary antigen test. Our objective was to evaluate the impact of the concomitant decrease in underdiagnosis on established and unknown risk factors for LD.

Prospective case-control study.

From 1 July 1998 to 30 June 2001, 228 LD cases and 293 controls were included for a national case-control study. Patients were included upon notification provided that they fulfilled international criteria for confirmed LD.

A history of diabetes mellitus, current tobacco smoking, travelling abroad, spending one or more nights away from home not leaving the country and being a driver by profession were independent risk factors. LD patients who had travelled abroad during their incubation period differed from LD patients who had not. They appeared healthier than non- or domestic travellers with respect to a history of coronary disease, pulmonary disease, current use of corticosteroids or immunosuppressives and any medication. Also the environmental risk factors differed significantly for the two groups.

The finding of two distinct populations of LD patients calls for a differentiated preventive strategy.