Epidemic legionellosis in England and Wales 1979--1982.

National surveillance of legionnaires' disease in England and Wales identified 588 cases during the years 1979--1982. The majority of cases appeared to be sporadic but 32 clusters of two or more cases were recognised, 24 in association with hotels, seven with hospitals and one with a construction site. Reports (3 published and 3 unpublished) on the investigation and control of six outbreaks are reviewed. All six were found to be common source outbreaks; four hotel associated, one was nosocomial and one was associated with a construction site. Domestic water systems were implicated as sources in the four hotels and the hospital. The most effective control measure was found to be continuous chlorination of the water supply combined with raising the hot water temperature to 60 degrees C or more in the calorifier and at least 55 degrees C to a maximum of 60 degrees C at outlets. Raising hot water temperatures alone was not always completely successful as a control measure. Only in the construction site outbreak was a cooling water system shown to be the principal source of infection.