PICCADILLY-CIRCUS LEGIONNAIRES-DISEASE OUTBREAK

Background An outbreak of legionnaires' disease occurred in central Lo ndon in January and February 1989. An Infection Control Committee was established to investigate the outbreak and institute control measures . The objective of this paper is to describe the investigation and con trol of the outbreak. Methods An epidemiological survey and case-contr ol study were carried out. The subjects were cases of community acquir ed pneumonia associated with central London with onset of illness in J anuary and February 1989. Results Thirty-three confirmed cases, includ ing five deaths, and ten suspected cases, including three deaths, were identified with dates of onset from 1 January to 11 February. A clust ering of visits by cases to the vicinity of Piccadilly Circus was note d, and a case-control study demonstrated a strong association between illness and visits to this area in the two weeks before onset of sympt oms. The causative organism, Legionella pneumophila serogroup 1, was i solated from six patients. Legionella pneumophila of the same serogrou p was isolated from water samples from five wet cooling systems (cooli ng towers) in the area under investigation, but in only two systems wa s the organism indistinguishable by subtyping from the patients' strai ns. Many of the cooling towers examined were inadequately maintained, including one of the two above a building adjacent to Piccadilly Circu s from which a strain indistinguishable from the outbreak strain was i solated. All cooling towers in the area were shut down until inspected , and only allowed to restart after appropriate maintenance had been i nstigated. Conclusions This outbreak showed the continuing risk of leg ionnaires' disease posed by wet cooling systems, including cooling tow ers, and highlighted the need to assess this risk so that appropriate maintenance is carried out. Regulations have recently been introduced, under the Health and Safety at Work Act, requiring notification of al l wet cooling systems to the local authority to facilitate the investi gation of outbreaks of legionnaires' disease.