[Legionnaire's disease outbreak].

Background And Objective: To describe an outbreak of Legionella pneumophila serogroup 1 in Mataró, Catalunya, Spain, in August 2002. The source of the microorganism was a cooling tower.

Patients And Method: Prospective and observational study with analysis of epidemiological, clinical, and microbiological data.

Results: 151 patients were affected (62% male), with a mean age of 58.4 years old. Seven patients were classified as Pontiac Fever and 144 suffered from pneumonia. The diagnosis of pneumonia was confirmed in 79% of cases, was considered suspicious in 14% and probable in 7%. Forty per cent of patients were smokers and 53.5% had comorbidities, mainly diabetes mellitus (22%). Chief symptoms were fever (97%), chills and muscular pain (63% respectively), headache (54%) and cough (53%). Pulmonary condensation was the more frequent radiological feature (71%). Normal pulmonary exploration was observed in 38%. Forty-three per cent of cases were severely ill, and 16% of patients belonged to Fine's IV and V class. Antigenuria was the most important test for diagnosis, which confirmed 76% of cases. Legionella spp. was obtained in respiratory secretions of 10 patients. Molecular analysis confirmed clonality between respiratory microorganisms and that obtained in the cooling tower.

Conclusion: The outbreak involved an important number of subjects in a short period of time. Antigenuria was the most useful test. However, the isolation of L. pneumophila from patients permitted the prompt identification of microorganism's source in a cooling tower. The low mortality observed probably relates to a rapid diagnosis and its target treatment.