Piccadilly Circus legionnaires' disease outbreak

An outbreak of legionnaires' disease occurred in central London 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 control of the outbreak.

An epidemiological survey and case-control study were carried out. The subjects were cases of community acquired pneumonia associated with central London with onset of illness in January and February 1989.

Thirty-three confirmed cases, including five deaths, and ten suspected cases, including three deaths, were identified with dates of onset from 1 January to 11 February. A clustering of visits by cases to the vicinity of Piccadilly Circus was noted, and a case-control study demonstrated a strong association between illness and visits to this area in the two weeks before onset of symptoms. The causative organism, Legionella pneumophila serogroup 1, was isolated from six patients. Legionella pneumophila of the same serogroup was isolated from water samples from five wet cooling systems (cooling towers) in the area under investigation, but in only two systems was the organism indistinguishable by subtyping from the patients' strains. Many of the cooling towers examined were inadequately maintained, including one of the two above a building adjacent to Piccadilly Circus from which a strain indistinguishable from the outbreak strain was isolated. All cooling towers in the area were shut down until inspected, and only allowed to restart after appropriate maintenance had been instigated.

This outbreak showed the continuing risk of legionnaires' disease posed by wet cooling systems, including cooling towers, 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 all wet cooling systems to the local authority to facilitate the investigation of outbreaks of legionnaires' disease.