An outbreak of Legionnaires' disease in an inner city district: importance of the first 24 hours in the investigation.

OBJECTIVE

To present the main results of the investigation of an outbreak of Legionnaire's disease that occurred in an inner city district of Barcelona between 15 October and 15 November 2000.

METHODS

Epidemiological surveys of patients and environmental investigations were initiated on the day the first five cases were notified. Water samples and smears from cooling tower trays were taken for microbiological analysis. Maps of the distribution of cases and possible contamination foci were elaborated. Incidences were calculated for each census tract.

RESULTS

A total of 54 patients related to the outbreak were identified, with a case fatality rate of 5.5%. Incidence rate in the area closest to the cooling tower (6.40/1000) was significantly higher than that of the rest of the neighbourhood (2.23/1.000, RR 2.87, 95%CI 1.37-6.12, P = 0.0035). Cultures positive for Legionella pneumophila serogroup 1, subtypes Pontiac, Philadelphia or Allentown, were obtained from eight patients. On the 39th day of the investigation it was found that the strain isolated in one of the cooling towers coincided with the serogroup, subtype and molecular profiles identified in clinical samples.

CONCLUSIONS

Rapid coordination of clinicians, microbiologists, epidemiologists and environmentalists permitted the source of infection and the affected cases to be correlated within a few days.